generateDS -- Generate Data Structures from XML Schema

Author: Dave Kuhlman
Contact: dkuhlman (at) davekuhlman (dot) org
Address:
http://www.davekuhlman.org
revision:2.14a
date:October 18, 2014
copyright:Copyright (c) 2004 Dave Kuhlman. This documentation and the software it describes is covered by The MIT License: http://www.opensource.org/licenses/mit-license.php.
abstract:generateDS.py generates Python data structures (for example, class definitions) from an XML Schema document. These data structures represent the elements in an XML document described by the XML Schema. It also generates parsers that load an XML document into those data structures. In addition, a separate file containing subclasses (stubs) is optionally generated. The user can add methods to the subclasses in order to process the contents of an XML document.

Contents

1   Introduction

generateDS.py generates Python data structures (for example, class definitions) from an XML Schema document. These data structures represent the elements in an XML document described by the XML Schema. It also generates parsers that load an XML document into those data structures. In addition, a separate file containing subclasses (stubs) is optionally generated. The user can add methods to the subclasses in order to process the contents of an XML document.

The generated Python code contains:

The generated classes contain the following:

The generated subclass file contains one (sub-)class definition for each data representation class. If the subclass file is used, then the parser creates instances of the subclasses (instead of creating instances of the superclasses). This enables the user to extend the subclasses with "tree walk" methods, for example, that process the contents of the XML file. The user can also generate and extend multiple subclass files which use a single, common superclass file, thus implementing a number of different processes on the same XML document type.

This document explains (1) how to use generateDS.py; (2) how to use the Python code and data structures that it generates; and (3) how to modify the generated code for special purposes.

There is also support for packaging the code you generate with generateDS.py. See Packaging your code.

2   Where To find it

3   How to build and install it

3.1   Requirements

Lxml is used both by generateDS.py and by the code it generates. Lxml is available at the Python Package Index https://pypi.python.org/pypi/lxml/ and at the Lxml project home site http://lxml.de/.

Older versions of Python XML support can sometimes cause problems. If you receive a traceback that includes "_xmlplus", then you will need to remove that _xmlplus package.

3.2   Installation

De-compress the generateDS distribution file. Use something like the following:

tar xzvf generateDS-x.xx.tar.gz

Then, the regular Distutils commands should work:

$ cd generateDS-x.xx
$ python setup.py build
$ python setup.py install        # probably as root

4   Packaging your code

There is some support for packaging the code you generate with generateDS.py. This support helps you to produce a directory structure with places to put sample code, sample XML instance documents, and utility code for use with your generated module. It also assists you in using Sphinx to generate documentation for your module. The Sphinx support is especially useful when the schema used to generate code contains "annotation" elements that document complexType definitions.

Instructions on how to use it are here: How to package a generateDS.py generated library -- librarytemplate_howto.html

And the package building support itself is here: LibraryTemplate -- http://www.davekuhlman.org/librarytemplate-1.0a.zip. It is also included in the generateDS distribution package.

5   The command line interface -- How to use it

5.1   Running generateDS.py

Run generateDS.py with a single argument, the XML Schema file that defines the data structures. For example, the following will generate Python source code for data structures described in people.xsd and will write it to the file people.py. In addition, it will write subclass stubs to the file peoplesubs.py:

python generateDS.py -o people.py -s peoplesubs.py people.xsd

Here is the usage message displayed by generateDS.py:

Synopsis:
    Generate Python classes from XML Schema definition.
    Input is read from in_xsd_file or, if "-" (dash) arg, from stdin.
    Output is written to files named in "-o" and "-s" options.
Usage:
    python generateDS.py [ options ] <xsd_file>
    python generateDS.py [ options ] -
Options:
    -h, --help               Display this help information.
    -o <outfilename>         Output file name for data representation classes
    -s <subclassfilename>    Output file name for subclasses
    -p <prefix>              Prefix string to be pre-pended to the class names
    -f                       Force creation of output files.  Do not ask.
    -a <namespaceabbrev>     Namespace abbreviation, e.g. "xsd:".
                             Default = 'xs:'.
    -b <behaviorfilename>    Input file name for behaviors added to subclasses
    -m                       Generate properties for member variables
    -c <xmlcatalogfilename>  Input file name to load an XML catalog
    --one-file-per-xsd       Create a python module for each XSD processed.
    --output-directory="XXX" Used in conjunction with --one-file-per-xsd.
                             The directory where the modules will be created.
    --module-suffix="XXX"    To be used in conjunction with --one-file-per-xsd.
                             Append XXX to the end of each file created.
    --subclass-suffix="XXX"  Append XXX to the generated subclass names.
                             Default="Sub".
    --root-element="XX"      When parsing, assume XX is root element of
    --root-element="XX|YY"   instance docs.  Default is first element defined
                             in schema.  If YY is added, then YY is used as the
                             top level class; if YY omitted XX is the default.
                             class. Also see section "Recognizing the top level
                             element" in the documentation.
    --super="XXX"            Super module name in generated in subclass
                             module. Default="???"
    --validator-bodies=path  Path to a directory containing files that provide
                             bodies (implementations) of validator methods.
    --use-old-simpletype-validators
                             Use the old style simpleType validator functions
                             stored in a specified directory, instead of the
                             new style validators generated directly from the
                             XML schema.  See option --validator-bodies.
    --use-getter-setter      Generate getter and setter methods.  Values:
                             "old" - Name getters/setters getVar()/setVar().
                             "new" - Name getters/setters get_var()/set_var().
                             "none" - Do not generate getter/setter methods.
                             Default is "new".
    --user-methods= <module>,
    -u <module>              Optional module containing user methods.  See
                             section "User Methods" in the documentation.
    --no-dates               Do not include the current date in the generated
                             files. This is useful if you want to minimize
                             the amount of (no-operation) changes to the
                             generated python code.
    --no-versions            Do not include the current version in the
                             generated files. This is useful if you want
                             to minimize the amount of (no-operation)
                             changes to the generated python code.
    --no-process-includes    Do not process included XML Schema files.  By
                             default, generateDS.py will insert content
                             from files referenced by <include ... />
                             elements into the XML Schema to be processed.
    --silence                Normally, the code generated with generateDS
                             echoes the information being parsed. To prevent
                             the echo from occurring, use the --silence switch.
                             Also note optional "silence" parameter on
                             generated functions, e.g. parse, parseString, etc.
    --namespacedef='xmlns:abc="http://www.abc.com"'
                             Namespace definition to be passed in as the
                             value for the namespacedef_ parameter of
                             the export() method by the generated
                             parse() and parseString() functions.
                             Default=''.
    --external-encoding=<encoding>
                             Encode output written by the generated export
                             methods using this encoding.  Default, if omitted,
                             is the value returned by sys.getdefaultencoding().
                             Example: --external-encoding='utf-8'.
    --member-specs=list|dict
                             Generate member (type) specifications in each
                             class: a dictionary of instances of class
                             MemberSpec_ containing member name, type,
                             and array or not.  Allowed values are
                             "list" or "dict".  Default: do not generate.
    --export=<export-list>   Specifies export functions to be generated.
                             Value is a whitespace separated list of
                             any of the following:
                                 write -- write XML to file
                                 literal -- write out python code
                                 etree -- build element tree (can serialize
                                     to XML)
                             Example: "write etree"
                             Default: "write"
    -q, --no-questions       Do not ask questions, for example,
                             force overwrite.
    --session=mysession.session
                             Load and use options from session file. You can
                             create session file in generateds_gui.py.  Or,
                             copy and edit sample.session from the
                             distribution.
    --fix-type-names="oldname1:newname1;oldname2:newname2;..."
                             Fix up (replace) complex type names.
    --version                Print version and exit.

Usage example:

    $ python generateDS.py -f -o sample_lib.py sample_api.xsd

creates (with force over-write) sample_lib.py from sample_api.xsd.

    $ python generateDS.py -o sample_lib.py -s sample_app1.py \
            --member-specs=dict sample_api.xsd

creates sample_lib.py superclass and sample_app1.py subclass modules;
also generates member specifications in each class (in a dictionary).

The following command line options are recognized by generateDS.py:

o <filename>
Write the data representation classes to file filename.
s <filename>
Write the subclass stubs to file filename.
p <prefix>
Prepend prefix to the name of each generated data structure (class).
f
Force generation of output files even if they already exist. Do not ask before over-writing existing files.
a <namespaceabbrev>

Namespace abbreviation, for example "xsd:". The default is 'xs:'. If the <schema> element in your XML Schema, specifies something other than "xmlns:xs=", then you need to use this option. So, suppose you have the following at the beginning of your XSchema file:

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

Then you can the following command line option:

-a "xsd:"

But, note that generateDS.py also tries to pick-up the namespace prefix used in the XMLSchema file automatically. If the <schema> element has an attribute "xmlns:xxx" whose value is "http://www.w3.org/2001/XMLSchema", then generateDS.py will use "xxx:" as the alias for the XMLSchema namespace in the XMLSchema document.

b <behaviorfilename>
Input file name for behaviors to be added to subclasses. Specifies is the name of an XML document containing descriptions of methods to be added to subclasses generated with the -s flag. The -b flag requires the -s flag. See the section on XMLBehaviors below.
m
Generate property members and new style classes. Causes generated classes to inherit from class object. Generates a call to the built-in property function for each pair of getters and setters. This is experimental.
c <xmlcatalogfilename>
Specify the file to be used as an XML catalog. This file will be used by process_includes.py if needed to resolve references in <xs:import> and <xs:include> elements in the XML Schema. For more information on XML catalogs, see: http://en.wikipedia.org/wiki/XML_Catalog
one-file-per-xsd
Create a separate Python module for each XML Schema document processed (for example, using <xs:include> or <xs:import>). For help with using this option, see "One Per" -- generating separate files from imported/included schemas.
output-directory <directory>
When used with one-file-per-xsd, create generated output files in path <directory>.
module-suffix <suffix>
When used with one-file-per-xsd, append <suffix> to the end of each module name.
subclass-suffix=<suffix>

Append suffix to the name of classes generated in the subclass file. The default, if omitted, is "Sub". For example, the following will append "_Action" to each generated subclass name:

generateDS.py --subclass-suffix="_Action" -s actions.py mydef.xsd

And the following will append nothing, making the superclass and subclass names the same:

generateDS.py --subclass-suffix="" -s actions.py mydef.xsd
root-element=<element_name> -OR- <element_name>|<class_name>
Make element_name the assumed root of instance documents. The default is the name of the element whose definition is first in the XML Schema document. If class_name is also present (after a vertical bar), then class_name is assumed to be the name of the class to be created from the root (top level) element when parsing an XML instance document. If class_name is omitted, the default class name is the same as element_name. This flag effects the parsing functions (for example, parse(), parseString(), etc).
super=<module_name>

Make module_name the name of the superclass module imported by the subclass module. If this flag is omitted, the following is generated near the top of the subclass file:

import ??? as supermod

and you will need to hand edit this so the correct superclass module is imported.

validator-bodies=<path>
Obtain the bodies (implementations) for validator methods for members defined as simpleType from files in directory specified by <path>. The name of the file in that directory should be the same as the simpleType name with an optional ".py" extension. If a file is not provided for a given type, an empty body (pass) is generated. In these files, lines with "##" in the first two columns are ignored and are not inserted.
use-old-simpletype-validators

generateDS.py is capable of generating validator bodies -- the code that validates data content in an XML instance docuement and writes out warning messages if that data does not satisfy the facets in the xs:restriction in the xs:simpleType defintion in the XML schema. Use this option if you want to use your own validation bodies/code defined in a specified directory . See option --validator-bodies for information on that. Without this option (--use-old-simpletype-validators), the validator code will be generated directly from the XML schema, which is the default.

This option can also be used to generate code that does no validation. See simpleType and validators and Turning off validation of simpleType data for more information.

use-getter-setter

generateDS.py now generates getter and setter methods (for variable "abc", for example) with the names get_abc() and set_abc(), which I believe is a more Pythonic style, instead of getAbc() and setAbc(), which was the old behavior. Use this flag to generate getters and setters in the old style (getAbc() and setAbc()) or the newer style(get_abc() and set_abc()) which is the default or to omit generation of getter and setter methods. Possible values are:

  • "old" - Name getters/setters getVar()/setVar().
  • "new" - Name getters/setters get_var()/set_var().
  • "none" - Do not generate getter/setter methods.

The default is "new".

u, user-methods=<module>
If specified, generateDS.py will add methods to generated classes as specified in the indicated module. For more information, see section User Methods.
no-dates
Do not include the current date in the generated files. This is useful if you want to minimize the amount of (no-operation) changes to the generated python code.
no-versions
Do not include the current version in the generated files. This is useful if you want to minimize the amount of (no-operation) changes to the generated python code.
no-process-includes
Do not process included XML Schema files. By default, generateDS.py will insert content from files referenced by <include ... /> elements into the XML Schema to be processed. See section Include file processing. Note that include processing, which is performed in process_includes.py is required for generating validator bodies from the XML schema, because the Lxml ElementTree produced in process_includes.py is needed to generate the validator code. So, using this option also turns off automatic generation of validator code.
silence
Normally, the code generated with generateDS echoes the information being parsed. To prevent the echo from occurring, use the --silence switch. This switch causes generateDS.py, when it generates boiler-plate parsing functions, (parse(), parseString(), parseLiteral()), to generate code that does not print out output (export output to stdout).
namespacedef="<http://...>"
Namespace definition to be passed in as the value for the namespacedef_ parameter of the export() method by the generated parse() and parseString() functions. If this parameter is specified, then the export function will insert a namespace prefix definition attribute in the top-most (outer-most) element. (Actually, you can insert any attribute.) The default is an empty string.
external-encoding=<encoding>
If an XML instance document contains character data or attribute values that are not in the ASCII character set, then that data will not be written out correctly or will throw an exception. This flag enables the user to specify a character encoding into which character data will be encoded before it is written out by the export functions. The generated export methods encode data using this encoding. The default value, if this flag is omitted, is the value returned by sys.getdefaultencoding(). You can find a list of standard encodings here: http://docs.python.org/library/codecs.html#id3. Example use: --external-encoding='utf-8'.
member-specs
Generate member (type) specifications in each class: a dictionary of instances of class MemberSpec_ containing member name, type, and array or not. See User Methods section for more information about MemberSpec_. Allowed values are "list" or "dict". Default: do not generate member specifications (unless --user-methods specified).
export

Specify which of the export related member methods are to be generated. The value is a whitespace separated list of any of the following:

  • write -- Generate methods export, exportAttributes, and exportChildren. These methods write XML to a file.
  • literal -- Generate methods exportLiteral, exportLiteralAttributes and exportLiteralChildren. These methods write out python code.
  • etree -- Generate method to_etree. This method builds an lxml element tree, which can, for example, be serialized to XML using lxml's tostring function and searched with the lxml xpath capability. You can also iterate over nodes in the tree with the node's getiterator, iterchildren, etc, and use any of lxml's other capabilities.

For example: --export="write etree" and --export="write". The default is: --export="write literal".

q, no-questions
Do not ask questions. For example, if the "-f" command line option is omitted and the ouput file exists, then generateDS.py will not ask whether the file should be overwritten. (In this case, when "-q" is used, the "-f" must be used to force the output file to be written.
session=mysession.session
Load and use options from session file. You can create a session file in generateds_gui.py, the graphical front-end for generateDS.py. Additional options on the command line can be used to override options in the session file. A session file is an XML document, so you can modify it with a text editor.
fix-type-names="oldname1:newname1;oldname2:newname2;..." Fix up

(replace) complex type names. Using this option will replace the following: (1) the 'name' attribute of a complexType; (2) the 'type' attribute of each element that refers to the type; and (3) the 'base' attribute of each extension that refers to the type. These fixups happen before information is collected from the schema for code generation. Therefore, using this option is effectively equivalent to copying your schema, then editing it with your text editor, then generating code from the modified schema. If a new name is not specified, the default is to replace the old name with the old name plus an added "xx" suffix. Examples:

$ generateDS.py --fix-type-names="type1:type1Aux"
$ generateDS.py --fix-type-names="type1;type2:type2Repl"
version
Print out the current version of generateDS.py and immediately exit.

5.2   Name conflicts

5.2.1   Conflicts with Python keywords

In some cases the element and attribute names in an XML document will conflict with Python keywords. There are two solutions to fixing and avoiding name conflicts:

  • In an attempt to avoid these clashes, generateDS.py contains a table that maps names that might clash to acceptable names. This table is a Python dictionary named NameTable. The user can modify existing entries in this table within generateDS.py itself and add additional name-replacement pairs to this table, for example, if new conflicts occur.

  • Or, you can fix additional conflicts by following these steps:

    1. Create a module named generateds_config.py.

    2. Define a dictionary in that module named NameTable.

    3. Place additional name mappings in that dictionary. Here is a sample:

      NameTable = {
          'range': 'rangeType',
          }
      
    1. And, place that module where generateDS.py can import it, or place the directory containing that module on your PYTHONPATH environment variable.

    generateDS.py will attempt to import that module (generateds_config.py) and will add the name mappings in it to the default set of mappings in NameTable in generateDS.py itself.

5.2.2   Conflicts between child elements and attributes

In some cases the name of a child element and the name of an attribute will be the same. (I believe, but am not sure, that this is allowed by XML Schema.) Since generateDS.py treats both child elements and attributes as members of the generated class, this is a name conflict. Therefore, where such conflicts exist, generateDS.py modifies the name of the attribute by adding "_attr" to its name.

6   The graphical user interface -- How to use it

Here are a few notes on how to use the GUI front-end.

7   Common problems

7.1   Namespace prefix mis-match

generateDS.py is not very intelligent about detecting what prefix is used in the schema file for the XML Schema namespace. When this problem occurs, you may see the following when running generateDS.py:

AttributeError: 'NoneType' object has no attribute 'annotate'

generateDS.py assumes that the XML Schema namespace prefix in your schema is "xs:".

So, if the XML Schema namespace prefix in your schema is not "xs:", you will need to use the "-a" command line option when you run generateDS.py. Here is an example:

generateDS.py -a "xsd:" --super=mylib -o mylib.py -s myapp.py someschema.xsd

8   Supported features of XML Schema

The following constructs, among others, in XML Schema are supported:

See file people.xsd for examples of the definition of data types and structures. Also see the section on The XML Schema Input to generateDS.

8.1   Attributes + no nested children

Element definitions that contain attributes but no nested child elements provide access to their data content through getter and setter methods getValueOf_ and setValueOf_ and member variable valueOf_.

8.2   Mixed content

Elements that are defined to contain both text and nested child elements have "mixed content". generateDS.py provides access to mixed content, but the generated data structures (classes) are fundamentally different from that generated for other elements. See section Mixed content for more details.

Note that elements defined with attributes but with no nested sub-elements do not need to be declared as "mixed". For these elements, character data is captured in a member variable valueOf_, and can be accessed with member methods getValueOf_ and setValueOf_.

8.3   anyAttribute

generateDS.py supports anyAttribute. For example, if an element is defined as follows:

<xs:element name="Tool">
   <xs:complexType>
      <xs:attribute name="PartNumber" type="xs:string" />
      <xs:anyAttribute processContents="skip" />
   </xs:complexType>
</xs:element>

Then generateDS.py will generate a class with a member variable anyAttributes_ containing a dictionary. Any attributes found in the instance XML document that are not explicitly defined for this element will be stored in this dictionary. generateDS.py also generates getters and setters as well as code for parsing and export. generateDS.py ignores processContents. See section anyAttribute for more details.

8.4   Element extensions

generateDS.py now generates subclasses for extensions, that is when an element definition contains something like this:

<xs:extension base="sometag">

Limitation -- There is an important limitation, however: member names duplicated (overridden ?) in an extension generate erroneous code. Sigh. I guess I needed something more to do.

Several of the generated methods have been refactored so that subclasses can reuse the code in their superclasses. Take a look at the generated code to learn how to use it.

The Python compiler/interpreter requires that it has seen a superclass before it sees the subclass that uses it. Because of this, generateDS.py delays generating a subclass until after its superclass has been generated. Therefore, the order in which classes are generated may be different from what you expect.

8.5   Attribute groups

generateDS.py now handles definition and use of attribute groups. For example: the use of something like the following:

<xs:attributeGroup name="favorites">
    <xs:attribute name="fruit" />
    <xs:attribute name="vegetable" />
</xs:attributeGroup>

And, a reference or use like the following:

<xs:element name="person">
    <xs:complexType mixed="0">
        <xs:attributeGroup ref="favorites" />
        o
        o
        o

Results in generation of class person that contains members fruit and vegetable.

Multiple levels of attributeGroups are supported, that is, attribute groups themselves can contain references to other attribute groups.

8.6   Substitution groups

generateDS.py now handles a limited range of substitution groups, but, there is an important limitation, in particular generateDS.py handles substitution groups that involve complex types, but does not handle those that involve (substitute for) simple types (for example, xs:string, xs:integer, etc). This is because the code generated for members defined as simple types does not provide the needed information to handle substitution groups.

8.7   Primitive types

generateDS.py supports some, but not all, simple types defined in "XML Schema Part 0: Primer Second Edition" ( http://www.w3.org/TR/xmlschema-0/. See section "Simple Types" and appendix B). Validation is performed for some simple types. When performed, validation is done while the XML document is being read and instances are created.

Here is a list of supported simple types:

  • xs:string -- No validation.
  • xs:token -- No validation. White space between tokens is coerced to a single blank between tokens.
  • xs:integer, xs:short, xs:long. xs:int -- All treated the same. Checked for valid integer.
  • xs:float, xs:double, xs:decimal -- All treated the same. Checked for valid float.
  • xs:positiveInteger -- Checked for valid range (> 0).
  • xs:nonPositiveInteger -- Checked for valid range (<= 0).
  • xs:negativeInteger -- Checked for valid range (< 0).
  • xs:nonNegativeInteger -- Checked for valid range (>= 0).
  • xs:date, xs:dateTime -- All treated the same. No validation.
  • xs:boolean -- Checked for one of 0, false, 1, true.

8.8   simpleType

generateDS.py generates minimal support for members defined as simpleType. However, the code generated by generateDS.py does not enforce restrictions. For notes on how to enforce restrictions, see section simpleType and validators.

A simpleType can be a restriction on a primitive type or on a defined element type. So, for example, the following will generate valid code:

<xs:element name="percent">
    <xs:simpleType>
        <xs:restriction base="xs:integer">
            <xs:minInclusive value="1"/>
            <xs:maxInclusive value="100"/>
        </xs:restriction>
    </xs:simpleType>
</xs:element>

And, the following will also generate valid code:

<xs:simpleType name="emptyString">
    <xs:restriction base="xs:string">
        <xs:whiteSpace value="collapse"/>
    </xs:restriction>
</xs:simpleType>

<xs:element name="merge">
    <xs:complexType>
        <xs:simpleContent>
            <xs:extension base="emptyString">
                <xs:attribute name="fromTag" type="xs:string"/>
                <xs:attribute name="toTag" type="xs:string"/>
            </xs:extension>
        </xs:simpleContent>
    </xs:complexType>
</xs:element>

8.9   List values, optional values, maxOccurs, etc.

For elements defined with maxOccurs="unbounded", generateDS.py generates code that processes a list of elements.

For elements defined with minOccurs="0" and maxOccurs="1", generateDS.py generates code that exports an element only if that element has a (non-None) value.

8.10   simpleType and validators

8.10.1   Generating validator bodies from XML schema

If you do not use the --use-old-simpletype-validators command line option, then generateDS.py will generate validation code directly from the restrictions specified inside the simpleType definitions in your XML schema.

8.10.2   User written validator bodies

Here are a few notes that should help you write your own validator methods to enforce restrictions.

  • Default behavior -- The generated code, by default, treats the value of a member whose type is a simpleType as if it were declared as type xs:string.

  • Validator method stubs -- For a member variable name declared as a simpleType named X, a validator method validate_X is generated. Example -- from:

    <xs:simpleType name="tAnyName">
        <xs:restriction base="xs:string"/>
    </xs:simpleType>
    

    The class generated by generateDS.py will contain the following method definition:

    def validate_tAnyName(self, value):
        # Validate type tAnyName, a restriction on xs:string.
        pass
    
  • Calls to validator methods -- For a member variable declared as a simpleType X, a call to validate X is added to the build method. Example -- from:

    <xs:element name="person">
        <xs:complexType mixed="0">
            <xs:sequence>
                <xs:element name="test2" type="tAnyName"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    

    generateDS.py produces the following call:

    self.validate_tAnyName(self.test2)    # validate type tAnyName
    
  • Code bodies for validator methods can be added either (1) manually or (2) automatically from an external source. See command line option "--validator-bodies" and see below.

You can add code to the validator method stub to enforce the restriction for the base type and further restrictions imposed on that base type. This can be done in the following ways:

  1. Add code manually after generation. I recommend that you use the "-s" command line option and override the validator method in the resulting subclass file.
  2. Or, supply code bodies (implementations) in an external source and ask generateDS.py to insert those code bodies into generated validator methods. Here are notes on how to do this:
    • Use the "--validator-bodies=path" command line option to specify a directory.
    • In that directory, provide one file for each simpleType. The name of the file should be the same as the name of the simpleType with an optional extension ".py". generateDS.py looks for a file named type_name.py, first, and if not found, looks for a file named type_name.
    • If the "--validator-bodies" is not on the command line or neither type_name.py nor type_name is found, an empty body (a pass statement) is generated.
    • Lines from the file are inserted as is, except that lines containing "##" in the first two columns are omitted. Note that you will need to provide the correct indentation for a method in a class, specifically 8 spaces.

The support for simpleType in generateDS.py has the following limitations (among others, I'm sure):

  • It only works for simpleType defined with and referenced through a name. It does not work for "in-line" definitions. So, for example, the following works:

    <xs:element name="person">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="test3" type="tAnyName"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    
    <xs:simpleType name="tAnyName">
        <xs:restriction base="xs:string"/>
    </xs:simpleType>
    

    But, the following does not work:

    <xs:element name="person">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="test3">
                    <xs:simpleType name="tAnyName">
                        <xs:restriction base="xs:string"/>
                    </xs:simpleType>
                </xs:element>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
    
  • Attributes defined as a simple type are not supported.

8.10.3   Turning off validation of simpleType data

If you do not want validation performed on simpleType data, you have these options:

  1. When generating your code, use the --use-old-simpletype-validators command line option but do not use the --validator-bodies command line option. This will result in validator methods that have empty bodies (only a pass statement).
  2. Or, when you run your generated code, set the variable Validate_simpletypes_ to False. This variable is near the top of your generated module. This variable can be set to True or False before and during processing to turn validation on and off.

8.10.4   Additional notes on simpleType validation

Don't forget that xmllint can also be used to perform validation against the XML scheme. This validation includes checking against simpleType restrictions. See http://xmlsoft.org/ for more information on xmllint.

8.11   Include file processing

By default, generateDS.py will insert content from files referenced by include elements into the XML Schema to be processed. This behavior can be turned off by using the "--no-process-includes" command line option.

include elements are processed and the referenced content is inserted in the XML Schema by importing and using process_includes.py, which is included in the generateDS.py distribution.

process_includes.py will use either lxml or ElementTree, but its preference is lxml because lxml attempts to preserve namespace prefixes. So if your XML Schemas have <include ... /> elements in them, you might want to consider installing lxml, even though ElementTree is in the Python standard library for Python versions >= 2.5.

The include file processing is capable of retrieve included files via FTP and HTTP internet protocols as well as from the local file system.

9   The XML schema input to generateDS

Note: Quite a bit of work has been done on generateDS.py since this section was written. So, it accepts and processes more of features in XML Schema than earlier. The best advice is to give it a try on your schema. If it works, great. If it does not, post a message to the list: generateds-users -- https://lists.sourceforge.net/lists/listinfo/generateds-users.

generateDS.py actually accepts a subset of XML Schema. The sample XML Schema file should give you a picture of how to describe an XML file and the Python classes that you will generate. And here are some notes that should help:

Here are a few additional rules that will help you to write XML Schema files for generateDS.py:

9.1   Additional constructions

Here are a few additional constructions that generateDS.py understands.

9.1.1   <complexType> at top-level

You can use the <complexType> element at top level (instead of <element>) to define an element. So, for example, instead of:

<xs:element name="server-type">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="server-name" type="xs:string"/>
            <xs:element name="server-description" type="xs:string"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>

you can use the following, which is equivalent:

<xs:complexType name="server-type">
    <xs:sequence>
        <xs:element name="server-name" type="xs:string"/>
        <xs:element name="server-description" type="xs:string"/>
    </xs:sequence>
</xs:complexType>

9.1.2   Use of "ref" instead of "name" and "type" attributes

You can use the "ref" attribute to refer to another element definition, instead of using the "name" and "type" attributes. So, for example, you can use the following:

<xs:element name="server-info">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="server-comment" type="xs:string"/>
            <xs:element ref="server-type" />
        </xs:sequence>
    </xs:complexType>
</xs:element>
   in place of this:
<xs:element name="server-info">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="server-comment" type="xs:string"/>
            <xs:element name="server-type" type="server-type"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>

9.1.3   Extension types

generateDS.py generates a subclass for each element that that is defined as the extension of a base element. So, for the following:

<xs:complexType name="BType">
    <xs:complexContent>
        <xs:extension base="AType">
            <xs:sequence>
                o
                o
                o

generateDS.py will generate something like the following:

class BType(AType):
    o
    o
    o

9.1.4   Elements containing mixed content

generateDS.py generates special code to handle elements defined as containing mixed content, that is elements defined with attribute mixed="true". See section Mixed content for more details.

10   XMLBehaviors

With the use of the "-b" command line option, generateDS.py will also accept as input an XML document instance that describes behaviors to be added to subclasses when the subclass file is generated with the "-s" command line option.

An example is provided in the Demos/Xmlbehavior sub-directory of the distribution.

The XMLBehaviors capability in generateDS.py was inspired and, for the most part, designed by gian paolo ciceri (gp.ciceri@suddenthinks.com). This work is part of our work on our application development project for Quixote.

10.1   The XMLBehaviors input file

This section describes the XMLBehavior XML document that is used as input to generateDS.py. The XMLBehavior XML document is an XML instance document (given as an argument to the "-b" command line flag) that describes behaviors (methods) to be added to class definitions in the subclass file (generated with the "-s" command line flag).

See file xmlbehavior_po.xml in the Demos/Xmlbehavior directory in the distribution for an example that you can use as a model.

The elements in the XMLBehavior document type are the following:

  • <xb:xml-behavior> -- The base element in the document.
    • <xb:base-impl-url> -- The root (left-most portion) of URL containing implementation bodies. Implementation URLs are appended to this base URL.
    • <xb:behaviors> -- A list of behaviors.
      • <xb:behavior> -- Describes a single XMLBehavior.
        • <xb:class> -- The name of the class to which this behavior is to be added.
        • <xb:name> -- The name of the behavior/method. Must conform to Python name syntax.
        • <xb:args> -- A list of arguments to the behavior/method.
          • <xb:arg> -- A positional argument to the method.
            • <xb:name> -- The name of the argument.
            • <xb:data-type> -- The data-type of the argument.
        • <xb:return-type> -- The data-type of the value returned by the behavior/method.
        • <xb:impl-url> -- The URL of the implementation body. This value will be concatenated to the right-hand side of the base-impl-url.
        • <xb:ancillaries> -- A list of ancillary behaviors/methods. Each ancillary has a role, which defines how it is to be used.
          • <xb:ancillary> -- A specification of an ancillary behavior/method.
            • <xb:name> -- The name of the behavior/method. Must conform to Python name syntax.
            • <xb:role> -- The method's role. The following values are supported:
              • "DBC-precondition" -- A Design By Contract-style pre-condition check. This method will be called before the core behavior/method itself.
              • "DBC-postcondition" -- A Design By Contract-style post-condition check. This method will be called after the core behavior/method itself.
            • <xb:args> -- A list of arguments to the ancillary behavior/method. The element has the same content as the <xb:args> element for the core behavior/method.
            • <xb:return-type> -- The data-type of the value returned by the behavior/method.
            • <xb:impl-url> -- The URL of the implementation body. This value will be concatenated to the right-hand side of the base-impl-url.

10.2   Implementing other sources for implementation bodies

generateDS.py contains a function get_impl_body() that implements the ability to retrieve implementation bodies. The current implementation retrieves implementation bodies from an Internet Web URL. Other sources for implementation bodies can be implemented by modifying get_impl_body().

As an example, the version that follows first tries to retrieve an implementation body from a Web address and, if that fails, attempts to obtain the implementation body from a file in the local file system using the <xb:base-impl-url> as a path to a directory containing files, each of which contains one implementation body and <xb:impl-url> as the file name. This implementation of get_impl_body was provided by Colin Dembovsky of Systemsfusion Inc. Thanks, Colin. (I've included it in the generateDS.py script, but commented out, for those who want to use and possibly extend it.):

def get_impl_body(classBehavior, baseImplUrl, implUrl):
    impl = '        pass\n'
    if implUrl:
        trylocal = 0
        if baseImplUrl:
            implUrl = '%s%s' % (baseImplUrl, implUrl)
        try:
            implFile = urllib2.urlopen(implUrl)
            impl = implFile.read()
            implFile.close()
        except:
            trylocal = 1
        if trylocal:
            try:
                implFile = file(implUrl)
                impl = implFile.read()
                implFile.close()
            except:
                print '*** Implementation at %s not found.' % implUrl
    return impl

11   Additional features

Here are additional features, contributed by users such as Chris Allan. Many thanks.

11.1   xsd:list element support

xsd:list elements can be used with a child xsd:simpleType which confuses the XschemaHandler stack unrolling. xsd:list element support should allow the following XML Schema definition to be supported in generateDS.py:

<xsd:attribute name="Foo">
    <xsd:simpleType>
        <xsd:list>
            <xsd:simpleType>
                ...
            </xsd:simpleType>
        </xsd:list>
    </xsd:simpleType>
</xsd:attribute>

11.2   xsd:enumeration support

The enumerated values for the parent element are resolved and made available through the instance attribute values.

11.3   xsd:union support

In order to properly resolve and query types which are unions in an XML Schema, an element's membership in an xsd:union is available through the instance attribute unionOf.

11.4   Extended xsd:choice support

When a parent xsd:choice is exists, an element's "maxOccurs" and "minOccurs" values can be inherited from the xsd:choice rather than the element itself. xsd:choice elements have been added to the child element via the choice instance attribute and are now used in the "maxOccurs" and "minOccurs" attribute resolution. This should allow the following XML Schema definition to be supported in generateDS.py:

<xsd:element name="Foo">
    <xsd:complexType>
        <xsd:choice maxOccurs="unbounded">
            <xsd:element ref="Bar"/>
            <xsd:element ref="Baz"/>
        </xsd:choice>
    </xsd:complexType>
</xsd:element>

11.5   Arity, minOccurs, maxOccurs, etc

Some applications require information about the "minOccurs" and "maxOccurs" attributes in the XML Schema. Some of that information can be obtained by using the --member-specs= (list|dict) command line option, then looking at the member_data_items_ class variable that it generates in each data representation class. In particular, look at the get_container method (from class MemberSpec_).

11.6   More thorough content type and base type resolution

The previous content type and base type resolution is insufficient for some needs. Basically it was unable to handle more complex and shared element and simpleType definitions. This support has been extended to more correctly resolve the base type and properly indicate the content type of the element. This should provide the ability to handle more complex XML Schema definitions in generateDS.py. Documentation on the algorithm for how this is achieved is available as comments in the source code of generateDS.py -- see comments in method resolve_type in class XschemaElement.

11.7   Making top level simpleTypes available from XschemaHandler

Some developers working to extend the analysis and code generation in generateDS.py may be helped by additional information collected during the parsing of the XML Schema file.

Some applications need all the top level simpleTypes to be available for further queries after the SAX parser has completed its work and after all types have been resolved. These types are available as an instance attribute topLevelSimpleTypes inside XschemaHandler.

11.8   Namespaces -- inserting namespace definition in exported documents

In some cases, the document produced by a call to an export method will contain elements that have namespace prefixes. For example, the following snippet contains namespace prefix "abc":

<abc:people >
    <abc:person>
    o
    o
    o
    </abc:person>
</abc:people>

A way is needed to insert a namespace prefix definition into the generated document. Here is how generateDS.py fills that need.

Each generated export method takes an optional argument namespacedef_. If provided, the value of that parameter is inserted in the exported element. So, for example, the following call:

people.export(sys.stdout, 0,
    namespacedef_='xmlns:abc="http://www.abc.com/namespace"')

might produce:

<abc:people xmlns:abc="http://www.abc.com/namespace">
    <abc:person>
    o
    o
    o
    </abc:person>
</abc:people>

If this is an issue for you, then you may also want to consider using the "--namespacedef" command line option when you run generateDS.py. The value of this option will be passed in to the export function in the generated parse functions. So, for example, running generateDS.py as follows:

generateDS.py --namespacedef='xmlns:abc="http://www.abc.com/namespace.xsd"'
    -o mylib.py -s myapp.py myschema.xsd

will generate parse methods that automatically add the namespacedef_ argument to the call to export.

11.9   Support for xs:any

There is minimal support for the xs:any wild card declaration. Effectively, an element defined by an xs:complexType containing xs:any can contain any element type as a child element. Because generateDS.py does not know how to generate code to handle specific element types during the parsing and building of an XML instance document, it generates a call to a method gds_build_any in the GeneratedsSuper class. This method has a default implementation in the generated code. If your XML schema uses xs:any, you may need to add some code to that default implementation of gds_build_any. See section Overridable methods for guidance on how to provide an implementation of that method.

For more help with this, look at the code generated from an XML schema that uses xs:any. In particular, look at the code generated in the Python class corresponding to the xs:complexType containing xs:any and look at the default implementation of method gds_build_any in class GeneratedsSuper. Reading the code in the buildChildren and exportChildren methods of a class containing a child declared with xs:any should help you understand what is going on.

When you starting developing your implementation of gds_build_any, look at the code generated in several buildChildren methods. It's likely that you will be able to copy, paste, and edit code from there.

11.10   Generating Lxml Element tree

Once you have build the tree of objects that are instances of the classes generated by generateDS.py, you can use this to produce a tree of instances of the Lxml Element instances. See http://lxml.de/ for more about Lxml. And, see the function parseEtree in the generated code for an example of how to produce the Lxml Element tree:

def parseEtree(inFileName):
    doc = parsexml_(inFileName)
    rootNode = doc.getroot()
    rootTag, rootClass = get_root_tag(rootNode)
    if rootClass is None:
        rootTag = 'test'
        rootClass = Test
    rootObj = rootClass.factory()
    rootObj.build(rootNode)
    # Enable Python to collect the space used by the DOM.
    doc = None
    mapping = {}
    rootElement = rootObj.to_etree(None, name_=rootTag, mapping_=mapping)
    reverse_mapping = rootObj.gds_reverse_node_mapping(mapping)
    content = etree_.tostring(
        rootElement, pretty_print=True,
        xml_declaration=True, encoding="utf-8")
    sys.stdout.write(content)
    sys.stdout.write('\n')
    return rootObj, rootElement, mapping, reverse_mapping

11.10.1   Mapping generateDS objects to Lxml Elements and back

Now suppose that you have produced the tree of instances of the generated classes, and suppose that you have used that to produce a tree of instances of the Element class from Lxml. It may be useful to have a dictionary that maps instances in one tree to the corresponding instances in the other. You can create that dictionary by passing an empty dictionary as the value of the optional parameter mapping_ in the call to the to_tree method. And, you can produce the reverse mapping by calling the convenience method gds_reverse_node_mapping from superclass GeneratedsSuper. Again, see the code above for an example.

12   How-to Use the generated source code

12.1   The parsing functions

The simplest use is to call one of the parsing functions in the generated source file. You may be able to use one of these functions without change, or can modify one to fit your needs. generateDS.py generates the following parsing functions:

  • parse -- Parse an XML document from a file.
  • parseString -- Parse an XML document from a string.

These parsing functions are generated in both the superclass and the subclass files. Note the call to the export method. You may need to comment out or un-comment this call to export according to your needs.

For example, if the generated source is in people.py, then, from the command line, run something like the following:

python people.py people.xml

Or, from within other Python code, use something like the following:

import people
rootObject = people.parse('people.xml')

12.2   Recognizing the top level element

It might be that the generated module, when parsing an XML instance document, does not, by default, recognize the top level (root) element in an instance document. This might happen because generateDS.py does not detect the correct top level element from the XML schema or because you need to use the generated module to parse instance documents that have different top level elements. If this is the case, you might pick and use one of the following strategies:

  1. In your schema, move the definition of the element type that defines the top level element in your instance documents to the top of the schema. By default, generateDS.py uses the first definition in the schema as the when constructing the generated parse function.

  2. Use the "--root-element" command line option to specify top level element. But, be aware that this only works if the tag name and type name of the top level element are the same.

  3. Modify the parse function in your generated module, replacing the class whose factory is called and the tag name passed in to the export method. For example, change:

    def parse(inFileName):
        doc = minidom.parse(inFileName)
        rootNode = doc.documentElement
        rootObj = type1.factory()
        rootObj.build(rootNode)
        # Enable Python to collect the space used by the DOM.
        doc = None
        sys.stdout.write('<?xml version="1.0" ?>\n')
        rootObj.export(sys.stdout, 0, name_="type1",
            namespacedef_='')
        return rootObj
    

    to:

    def parse(inFileName):
        doc = minidom.parse(inFileName)
        rootNode = doc.documentElement
        rootObj = type2.factory()
        rootObj.build(rootNode)
        # Enable Python to collect the space used by the DOM.
        doc = None
        sys.stdout.write('<?xml version="1.0" ?>\n')
        rootObj.export(sys.stdout, 0, name_="type2",
            namespacedef_='')
        return rootObj
    

    Notice that we've changed the two occurrences of "type1" to "type2".

  4. Using the generated parse function as a model, create a separate module that imports your generated module. In the parse function in your module, make a change similar to that suggested above. And, of course, add any additional code needed by your application.

  5. Write a separate module containing your own parse function that inspects the top level element of an input XML instance document and automatically determines which generated class should be used to parse it. Here is an example:

    #!/usr/bin/env python
    
    import sys
    from optparse import OptionParser
    from xml.dom import minidom
    import mygeneratedmodule as gendsmod
    
    def get_root_tag(node):
        tag = node.tagName
        tags = tag.split(':')
        if len(tags) > 1:
            tag = tags[-1]
        rootClass = None
        if hasattr(gendsmod, tag):
            rootClass = getattr(gendsmod, tag)
        return tag, rootClass
    
    def parse(inFilename, options):
        doc = minidom.parse(inFilename)
        rootNode = doc.documentElement
        rootTag, rootClass = get_root_tag(rootNode)
        rootObj = rootClass.factory()
        rootObj.build(rootNode)
        # Enable Python to collect the space used by the DOM.
        doc = None
        sys.stdout.write('<?xml version="1.0" ?>\n')
        rootObj.export(sys.stdout, 0, name_=rootTag,
            namespacedef_='')
        doc = None
        return rootObj
    
    USAGE_TEXT = """
        python %prog [options] <somefile.xml>"""
    
    def usage(parser):
        parser.print_help()
        sys.exit(1)
    
    def main():
        parser = OptionParser(USAGE_TEXT)
        (options, args) = parser.parse_args()
        if len(args) == 1:
            infilename = args[0]
            parse(infilename, options)
        else:
            usage(parser)
    
    if __name__ == "__main__":
        main()
    

    Notice the call to get_root_tag, which attempts to recognize the top level tag in the input XML document so that the parse function can parse and export it.

12.3   The export methods

The generated classes contain methods export and exportLiteral which can be called to export classes to several text formats, in particular to an XML instance document and a Python module containing Python literals. See the generated parse functions for examples showing how to call the export methods.

12.3.1   Method export

The export method in generated classes writes out an XML document that represents the instance that contains it and its child elements. So, for example, if your instance tree was created by one of the parsing functions described above, then calling export on the root element should reproduce the input XML document, differing only with respect to ignorable white space.

12.3.2   Method exportLiteral

generateDS.py generates Python classes that represent the elements in an XML document, given an Xschema definition of the XML document type. The exportLiteral method will export a Python literal representation of the Python instances of the classes that represent an XML document.

12.3.2.1   What It Does

When generateDS.py generates the Python source code for your classes, this new feature also generates an exportLiteral method in each class. If you call this method on the root (top-most) object, it will write out a literal representation of your class instances as Python code.

generateDS.py also generates a function at top level (parseLiteral) that parses an XML document and calls the "exportLiteral" method on the root object to write the data structure (instances of your generated classes) as a Python module that you can import to (re-)create instances of the classes that represent your XML document.

12.3.2.2   Why You Might Care

generateDS.py was designed and built with the assumption that we are not interested in marking up text content at all. What we really want is a way to represent structured and nested date in text. It takes the statement, "I want to represent nested data structures in text.", entirely seriously. Given that assumption, there may be times when you want a more "Pythonic" textual representation of the Python data structures for which generateDS.py has generated code. exportLiteral enables you to produce that representation.

This feature means that the classes that you generate from an XML schema support the interchangeability of XML and Python literals. This means that, given classes generated by generateDS.py for your XML document type, you can perform the following transformations:

  • Translate an XML document into a Python module containing a literal definition of the contents of the XML document.
  • Translate the literal definition of a Python data structure into an XML instance document.

This capability enables you to:

  • Work with an XML (text) document, then exchange it for a Python text representation of the content of that document.
  • Work with a Python literal text representation of your XML document, then exchange that for an XML document that represents the same content.
  • "Freeze" your XML document as a Python module that you can import. The module can be edited with your text editor, so perhaps it would be better to say that it is frozen, but not too hard. The classes that you generate with generateDS.py can be used to:
    1. Read in an XML document.
    2. (Optionally) modify the Python instances that represent that XML document.
    3. Write the instances out as a Python module that you can later import.

12.3.2.3   How to use it

See the generated function parseLiteral for an example of how to use exportLiteral.

12.3.3   Exporting compact XML documents

You can also export "compact" XML documents. A compact document is one that is exported without the ignorable whitespace that is used to produce pretty printed documents. In contrast, a pretty printed document will have leading white space on most lines to show indentation.

To produce compact documents, pass the optional argument pretty_print=False to the export function. Check the "parse" functions generated near the bottom of modules generated by generateDS.py, where pretty_print=True is passed in by default.

12.4   Building instances

If you have an instance of a minidom node that represents an element in an XML document, you can also use the 'build' member function to populate an instance of the corresponding class. Here is an example:

from xml.dom import minidom
from xml.dom import Node

doc = minidom.parse(inFileName)
rootNode = doc.childNodes[0]
people = []
for child in rootNode.childNodes:
    if child.nodeType == Node.ELEMENT_NODE and child.nodeName == 'person':
        obj = person()
        obj.build(child)
        people.append(obj)

12.5   Using the subclass module

If you choose to use the generated subclass module, and I encourage you to do so, you may need to edit and modify that file. Here are some of the things that you must do (look for "???"):

  • Edit the import statement at the top of the file. It should import the generated superclass file. Note that you can also use the "--super" command line option to insert this automatically.
  • Edit the USAGE_TEXT string so that it gives a help message appropriate for your use.
  • Edit the main function toward the bottom of the file. It should call a method, that you have possibly added, to the root subclass.

You can also (and most likely will want to) add methods to the generated classes. See the section How to Modify the Generated Code for more on this.

The classes generated from each element definition provide getter and setter methods to access its attributes and child elements.

Elements that are referenced but not defined (i.e. that are simple, for example strings, integers, floats, and booleans) are accessed through getter and setter methods in the class in which they are referenced.

12.6   Elements with attributes but no nested children

Element definitions that contain attributes but no nested child elements provide access to their data content through getter and setter methods getValueOf_ and setValueOf_ and member variable valueOf_.

12.7   Mixed content

The goal of generateDS.py is to support data structures represented in XML as opposed to text mark-up. However, it does provides some support for mixed content. But, for mixed content, the data structures and code generated by generateDS.py are fundamentally different from those for elements that do not contain mixed content.

There are limitations, of course. A known limitation is related to extension elements. Specifically, if an element contains mixed content, and this element extends a base class, then the base class and any classes it extends must be defined to contain mixed content. This is due to the fact that generateDS.py generates a data structure (class) for elements containing mixed content that is fundamentally different from that generated for other elements.

Here is an example of mixed content:

<note>This is a <bold>nice</bold> comment.</note>

When an element is defined with something like the following:

<xs:complexType mixed="true">
    <xs:sequence>
        o
        o
        o

then, instead of generating a class whose named members refer to nested elements, a class containing a list of instances of class MixedContainer is generated. In order to process the content of a mixed content element, the code you write will need to walk this list of instances of MixedContainer and check the type of each item in that list. Basically, the structure becomes more DOM-like in the sense that it has a list of children, rather than named fields.

Instances of MixedContainer have the following methods:

  • getCategory -- Returns one of the following, depending on the content:
    • CategoryText -- Text content.
    • CategorySimple -- Simple elements, that is, elements defined as xs:string, xs:integer, etc. For these, the member variable content_type, accessible through method getContenttype will contain one of TypeString, TypeInteger, TypeFloat, TypeDecimal, TypeDouble, or TypeBoolean.
    • CategoryComplex -- Complex elements represented by a generated class. For these, the member variable name, accessible through method getName will return the element/tag name and the member variable value, accessible through method getValue will return the instance.
  • getContenttype -- Returns one of TypeString, TypeInteger, TypeFloat, TypeDecimal, TypeDouble, or TypeBoolean. Valid only when category is CategorySimple.
  • getName -- For CategoryComplex, returns the name of the element.
  • getValue -- Returns the value of this chunk of content. Its type depends on the value returned by getCategory and getContenttype.

Note that elements defined with attributes but with no nested sub-elements do not need to be declared as "mixed". For these elements, character data is captured in a member variable valueOf_, and can be accessed with member methods getValueOf_ and setValueOf_.

12.8   anyAttribute

For elements that specify anyAttributes, generateDS.py produces a class containing the following:

  • A member variable anyAttributes_ containing a Python dictionary. After parsing an XML instance document, this dictionary will contain name-value pairs for any attributes in the instance document not explicitly defined for that element.
  • The following getters and setters: getAnyAttributes_ and setAnyAttributes_.
  • Code to export the attribute names and values stored in the dictionary.
  • Code to parse attributes in addition to those explicitly defined for the element and store them in the dictionary.

Note: Attributes that are explicitly defined for an element are not stored in the dictionary anyAttributes_.

generateDS.py ignores the processContents attribute on the anyAttribute element in the XML Schema

12.9   User Methods

generateDS.py provides a mechanism that enables you to attach user defined methods to specific generated classes. In order to do so, create a Python module containing specifications of those methods and indicate that module on the command line with the "--user-methods" option. Example:

python generateDS.py -f --super=people_sup -o people_sup.py -s people_sub.py --user-methods=gends_user_methods people.xsd

The module named with this flag must be located where generateDS.py can import it. You might need to add the directory containing your user methods module to the PYTHONPATH environment variable.

The module specified with the "--user-methods" flag should define a variable METHOD_SPECS which contains a list of instances of a class that implements methods match_name and get_interpolated_source.

See file gends_user_methods.py for an example of this specification file and the definition of class MethodSpec. Read the comments in that file for more guidance.

The member_data_items_ class variable -- User methods, especially those attached to more than one class, are likely to need a list of the members in the current class. Each generated class has a class variable containing a list of specifications of the members in the class. Each item in this list is an instance of class MemberSpec_, which is defined near the top of your generated (super-class) file. Use the following to access the information in each member specification:

  • m.get_name() -- Returns the name of the member variable (a string).

  • m.get_data_type() -- Returns the data type of the member variable (a string). If the data type is a list, returns the terminal type, which is that last string in the list. (Also see get_data_type_chain().)

  • m.get_data_type_chain() -- Returns the data type of the member variable (a string or list). When the data type is a simpleType that has another simpleType as it's base or is a complexType that extends a simpleType, then the data type is a list of strings, for example:

    ['RelationType', 'xs:string']
    

    The last string in the list is the terminal type, usually a built-in simple type. Note that m.get_data_type() returns the terminal (last) type.

  • m.get_container() -- (an integer) Indicates whether the member variable is a single item or a list/container (i.e. generated from maxOccurs > 0): 0 indicates a single item; 1 indicates a list.

There are a number of things of interest in this sample file (gends_user_methods.py):

  • Although, the MethodSpec class must be included in your user methods specification module, you can modify this class. For example, for special situations, it might be useful to modify either of the methods MethodSpec.match_name or MethodSpec.get_interpolated_source. These methods are called by generateDS.py. See comments on the definitions of these methods in gends_user_methods.py.

  • A method set_up is attached to the root class. (This user method specification module is intended to be used with people.xsd/people.xml in the Demos/People directory.) It performs initialization, before the walk method is called. In particular, set_up initializes a counter and imports the types module (which saves us from having to modify the generated code).

  • The walk_and_update and walk_and_show methods provide an example showing how to walk the entire document object tree.

  • The method walk_and_update uses the member_data_items_ class variable to obtain a list of members of the class. It's a list of instances of class MemberSpec_, which support the m.get_name(), m.get_data_type(), and m.get_container() methods described above.

  • In method walk_and_show, note the use of getattr to retrieve the value of a member variable and the use of setattr to set the value of a member variable.

  • The expression "%(class_name)s" is used to insert the class name into the generated source code.

  • Notice how the types module is used to determine whether a member variable contains a simple type or an instance of a class. Example:

    obj1 = getattr(self, member[0])
    if type(obj1) == types.InstanceType:
        ...
    
  • In string formatting operations, you will need to use double percent signs in order to "pass through" a single percent sign, for example:

    print '%%d. class: %(class_name)s  depth: %%d' %% (counter, depth, )
    

    where the single percent signs are interpolated ("%(class_name)s" is replace by the class name), and double percent signs are replace by single percent signs ("%%d" becomes "%d").

Suggestion -- How to begin:

  1. Make a copy of gends_user_methods.py.
  2. Modify the method specifications in that file. Replace the source code and the class_name pattern in each specification.
  3. Run generateDS.py with the "--user-methods" (or "-u") flag.
  4. Inspect the user methods in the generated classes.
  5. Test your generated code.
  6. Repeat as necessary.

12.10   Overridable methods

generateDS.py generates calls to several methods that each have a default implementation in a superclass. The default superclass with default implementations is included in the generated code. The user can replace this default superclass by implementing a module named generatedssuper.py containing a class named GeneratedsSuper.

What to look for in the generated code:

  • In the generated superclass file (generated with command line option "-o"), look for the import of module generatedssuper.py and the definition of the (default) class GeneratedsSuper.
  • Also look for calls to methods format_integer(), format_float(), format_double(), etc.

To view the default implementation of class GeneratedsSuper, look in a generated superclass module (one generated by the "-o" command line option with generateDS.py). The default definition of class GeneratedsSuper is near the top of a generated module.

If you wish to modify the behavior of any of these methods, see below for instructions on how to do so.

Caution: Overriding any of the *_format_*() methods enables you to export invalid XML. So, use at your own risk, test before using, etc.

How to modify the behavior of the default methods:

  • Implement methods that override the default methods.
  • Look at the definition of the default methods in class GeneratedsSuper in order to learn the signature of the methods in that class.
  • Look at the definition of the default methods to determine what they do and what type of value they return, then do something similar in your overriding method.
  • Search for and look at the call to the method you are interested in modifying (for example gds_format_string) to learn where and when it is used and for what.

Where to put (implement) methods that override the default methods -- You can place the implementations of methods that override the default methods in the following places:

  • In a class named GeneratedsSuper in a separate module named generatedssuper. Since this class would replace the default implementations, you should provide implementations of all the default methods listed above in that class. The distribution contains a generatedssuper.py which you can modify for your specific needs.

  • In individual generated (super) classes (the ones generated with the "-o" command line option) using the User Methods feature.

  • In individual classes in a subclass module generated with the "-s" command line option.

    If you want to use the same method in more than one generated subclass, then you might consider putting that method in a "mix-in" class and inherited that method in the generated subclass. With this approach, you must put the mix-in class containing your methods before the regular superclass, so that Python will find your custom methods before the default ones. That is, you must use:

    class clientSub(MySpecialMethods, supermod.client):
    

    not:

    class clientSub(supermod.client, MySpecialMethods):
    

If you choose to implement module generatedssuper, here are a few instructions and suggestions:

  • Implement a module generatedssuper.py containing definition of a class GeneratedsSuper. You can copy and paste the default implementation from a superclass module generated with the -o command line option for generateDS.py.

  • Put this module in a location where it can be imported when your generated code is run. Note the try:except: block in your generated superclass module that attempts to import it and that uses the default implementation of GeneratedsSuper when it cannot.

  • An easy way to begin is to copy the default definition of the class GeneratedsSuper from a superclass module generated with the "-o" command line option into a module named generatedssuper.py. Then modify your (copied) implementation.

  • To implement a method that does a task specific to particular class or a particular member of a class, do something like the following:

    def gds_format_string(self, input_data, input_name=''):
        if self.__class__.__name__ == 'person':
            return '[[%s]]' % input_data
        else:
            return input_data
    

    or:

    def gds_format_string(self, input_data, input_name=''):
        if self.__class__.__name__ == 'booster' and input_name == 'lastname':
            return '[[%s]]' % input_data
        else:
            return input_data
    

    Alternatively, to attach a method to a specific class, use the User Methods or a generated subclass module (command line option "-s"), as described above.

  • You can also add additional, new methods that you call (for example, in subclasses that you generate with the -s command line option for generateDS.py.

12.11   The element name to class name dictionary

generateDS.py automatically generates a dictionary that maps element/complexType names to the names of the class generated for that complexType definition. This dictionary is named GDSClassesMapping. You will find it in the module generated with the "-o" option.

13   "One Per" -- generating separate files from imported/included schemas

The --one-file-per-xsd command line option enables you to generate a separate Python module for each XML schema that is imported or included (using <xs:import> or <xs:include>) by a "master" schema. Then, in your Python application, these modules can then be imported separately. Alternatively, these modules can be placed in a Python package (a directory containing a file named "__init__.py"). See http://docs.python.org/2/tutorial/modules.html#packages for more on Python packages.

Here is a sample use:

$ ../generateDS.py --one-file-per-xsd --output-directory="OnePer" --module-suffix="One" one_per.xsd

The above command does the following:

Here are a few hints, guidelines, and suggestions:

14   How to modify the generated code

This section attempts to explain how to modify and add features to the generated code.

14.1   Adding features to class definitions

You can add new member definitions to a generated class. Look at the 'export' and 'exportLiteral' member functions for examples of how to access member variables and how to walk nested sub-elements.

Here are interesting places to look in each class definition:

  • The 'export' and 'exportLiteral' methods -- These methods walk the object tree. You can consider copying and renaming them to produce other tree walking methods.
  • The 'build' method -- These methods extract information from the minidom node. You can inspect the 'build' methods to learn how to extract information for other purposes.

And, if you need methods that are common to and shared by several of the generated subclasses, you can put them in a new class and add that class to the superclass list for each of your subclasses.

Although you can add your own methods to the generated superclasses, I'm recommeding that you add methods to the generated subclasses in the subclass module generated with the "-s" command line option, and then edit the subclass module in order to build your application. Why?

  • The superclasses are cluttered with other code. Using the subclass file enables you to keep your application code separate.
  • By putting your application code in the subclass file, you will be able to reuse the superclass file. You can generate multiple subclass files from the same XML Schema definition file. Each of these subclass files can import the same superclass file.

Here are some alternatives to using the subclass file:

  • Add more than one method to each generated (super-)class. Each method implements a separate task or "application". If the number of tasks grows, this will create maintenance difficulties, however.
  • Re-generate multiple (super-)class files. Add methods to the classes in these separate files to implement different tasks. This of course will not work well if you have had to modify the parser, for example, since generating the file.

15   Examples and demonstrations

Under the directory Demos are several examples:

Suggested uses:

15.1   Django -- Generating Models and Forms

generateDS.py can be used to generate Django models and Django forms that represent the data structures defined in an XML Schema.

Note: In order to use this capability, you must obtain the "source" distribution of generateDS.py. You can do this either (1) by downloading generateDS-x.xxy.tar.gz from the Python Package Index or (2) by downloading the distribution from Bitbucket at https://bitbucket.org/dkuhlman/generateds. In particular, installing generateDS.py using pip does not give you all the files you need in order to use this capability.

Note: You only need to obtain the source distribution (so that you can copy the files in the django/ directory, for example); you do not necessarily need to install from it. If you have already installed generateDS.py using pip or easy_install, you do not need to re-install from the source tree.

There are support files in the django directory in the source distribution (but not in the version install using pip or easy_install).

Here is an overview of the process:

  • Step 1. Generate bindings -- Run generateDS.py.
  • Step 2. Extract simpleType definitions from schema -- Run gends_extract_simple_types.py.
  • Step 3. Generate models.py and forms.py -- Run gends_generate_django.py.

The script gends_run_gen_django.py performs these three steps.

15.1.1   How to generate Django models and forms

Warning: Running this script attempts to over-write the following files in the current directory:

  • <schema>lib.py
  • generateds_definedsimpletypes.py
  • models.py
  • forms.py

To over-write these files, use the -f (or --force) command line option.

So, it's a good idea to create a separate, new directory in which to do the following work.

Now, follow these steps:

  1. Create an empty directory:

    $ mkdir WorkDir
    $ cd WorkDir
    
  2. Copy the files in from the sub directory django/ in the of the source distribution of generateDS.py to the current directory:

    $ cp /my_sources/generateDS-n.nn/django/* .
    
  3. Copy the file process_includes.py in the distribution to the current directory:

    $ cp /my_sources/generateDS-n.nn/process_includes.py .
    
  4. Run the following:

    $ ./gends_run_gen_django.py myschema.xsd
    
  5. Copy the generated files models.py and forms.py to your Django application.

15.1.2   How it works

Here are a few notes that might be helpful if and when you need to do some debugging or extend the current capabilities or write a new "meta-app" that uses the same approach but does something new and even entirely different.

gends_run_gen_django.py uses Popen to run other scripts, specifically, it runs generateDS.py, gends_extract_simple_types.py, and gends_generate_django.py.

gends_extract_simple_types.py scans the XML schema doc and extracts simpleType definitions. It writes descriptors of those definitions to the file generateds_definedsimpletypes.py.

gends_generate_django.py generates the models.py and forms.py files by calling the class method generate_model_ for each class in the list of classes in the variable __all__ in the generated bindings. __all__ is defined at the bottom of the generated bindings module.

The class method generate_model_ (along with some tables for predefined simple types etc) is defined in generatedssuper.py, which is imported by the generated bindings module. We are overriding the default version of that class. generate_model_ is defined in the class GeneratedsSuper, which is used as the root super class of all generated data representation classes.

16   Sample code and extensions

16.1   Capturing xs:date elements as dates

The following extension employs a user method (see User Methods) in order to capture elements defined as xs:date as date objects.

Thanks to Lars Ericson for this code and explanation.

By default, generateDS.py treats elements declared as type xs:date as though they are strings.

To get xs:dates stored as dates, in your local copy, add the following user method (User Methods), a slight modification of the sample (in gends_user_methods.py):

method1 = MethodSpec(name='walk_and_update',
    source='''\
    def walk_and_update(self):
        members = %(class_name)s.member_data_items_
        for member in members:
            obj1 = getattr(self, member.get_name())
            if member.get_data_type() == 'xs:date':
                newvalue = date_calcs.date_from_string(obj1)
                setattr(self, member.get_name(), newvalue)
            elif member.get_container():
                for child in obj1:
                    if type(child) == types.InstanceType:
                        child.walk_and_update()
            else:
                obj1 = getattr(self, member.get_name())
                if type(obj1) == types.InstanceType:
                    obj1.walk_and_update()
''',
    class_names=r'^.*$',
    )

Then, define date_calcs.py as:

#!/usr/bin/env python
# -*- mode: pymode; coding: latin1; -*-

import datetime

# 2007-09-01

# test="2007-09-01"
# print test
# print date_from_string(test)

def date_from_string(str):
    year = int(str[:4])
    month = int(str[5:7])
    day = int(str[8:10])
    dt = datetime.date(year, month, day)
    return dt

And, add a "str" here in generateDS.py:

def quote_xml(inStr):
    s1 = str(inStr)
    s1 = s1.replace('&', '&amp;')
    s1 = s1.replace('<', '&lt;')
    s1 = s1.replace('"', '&quot;')
    return s1

Also, add these imports to TEMPLATE_HEADER in generateDS.py:

import date_calcs
import types

17   Limitations of generateDS

17.1   XML Schema limitations

There are things in Xschema that are not supported. You will have to use a restricted sub-set of Xschema to define your data structures. See above for supported features. See people.xsd and people.xml for examples.

And, then, try it on your XML Schema, and let me know about what does not work.

17.2   Large documents

Warning -- This section describes an optional generated SAX parser which, I believe, is currently broken for all but the simplest schemas. Generation of a SAX parser has not been updated for the latest changes to generateDS.py. In particular, when names of elements are reused (in different parent elements), the SAX parser becomes confused. Until I've been able to figure out how to fix this, you are advised not to use the SAX parser.

generateDS.py generates two kinds of parsers: one kind is based on SAX and the other is build on minidom. See the generated functions saxParse, parse(), and parseString(). Using the SAX parser instead of the minidom parser should reduce memory requirements for large documents, since the minidom parser, but not the SAX parser, constructs a DOM tree for the entire document in memory.

However, both styles of parsers construct instances of the data structures generated by generateDS.py. This means that, even when the SAX parser is used, generateDS.py may not be well-suited for applications that read large XML documents, although what "large" means depends on your hardware. Notice that the minidom parsing functions (parse() and parseString()) over-write the variable doc so as to enable Python to reclaim the space occupied by the DOM tree, which may help alleviate the memory problem to some extent when the minidom parser is used.

18   Includes -- The XML schema include element

While generateDS.py itself does not process XML Schema include elements, the distribution provides a script process_includes.py that can be used as a preprocessor. This script scans your XML Schema document and, recursively, documents that are included looking for include elements; it inserts all content into a single document, which it writes out.

Since process_includes.py uses the ElementTree API, in order to use process_includes.py you will need one of the following:

Here are samples of how you might use process_includes.py, if your schema contains include elements.

Example 1:

$ python process_includes.py definitions1.xsd | \
$ python generateDS.py -f --super=task1sup -o task1sup.py -s task1sub.py -

Example 2:

$ python process_includes.py definitions1.xsd tmp.xsd
$ python generateDS.py -f --super=task1sup -o task1sup.py -s task1sub.py tmp.xsd

For help and usage information, run the following:

$ python process_includes.py --help

19   Acknowledgments

Many thanks to those who have used generateDS.py and have contributed their comments and suggestions. These comments have been valuable both in teaching me about things I needed to know in order to continue work and in motivating me to do the work in the first place.

And, a special thanks to those of you who have contributed patches for fixes and new features. Recent help has been provided by the following among others:

20   See also

Python: The Python home page.

Dave's Page: My home page, which contains more Python stuff.