13.5.1 XMLParser Objects

Python PEP

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13.5.1 XMLParser Objects

xmlparser objects have the following methods:

Parse( data[, isfinal]): Parses the contents of the string data, calling the appropriate handler functions to process the parsed data. isfinal must be true on the final call to this method. data can be the empty string at any time.

ParseFile( file): Parse XML data reading from the object file. file only needs to provide the read(nbytes) method, returning the empty string when there's no more data.

SetBase( base): Sets the base to be used for resolving relative URIs in system identifiers in declarations. Resolving relative identifiers is left to the application: this value will be passed through as the base argument to the ExternalEntityRefHandler, NotationDeclHandler, and UnparsedEntityDeclHandler functions.

GetBase( ): Returns a string containing the base set by a previous call to SetBase(), or None if SetBase() hasn't been called.

GetInputContext( ): Returns the input data that generated the current event as a string. The data is in the encoding of the entity which contains the text. When called while an event handler is not active, the return value is None. New in version 2.1.

ExternalEntityParserCreate( context[, encoding]): Create a ``child'' parser which can be used to parse an external parsed entity referred to by content parsed by the parent parser. The context parameter should be the string passed to the ExternalEntityRefHandler() handler function, described below. The child parser is created with the ordered_attributes, returns_unicode and specified_attributes set to the values of this parser.

UseForeignDTD( [flag])

Calling this with a true value for flag (the default) will cause Expat to call the ExternalEntityRefHandler with None for all arguments to allow an alternate DTD to be loaded. If the document does not contain a document type declaration, the ExternalEntityRefHandler will still be called, but the StartDoctypeDeclHandler and EndDoctypeDeclHandler will not be called.

Passing a false value for flag will cancel a previous call that passed a true value, but otherwise has no effect.

This method can only be called before the Parse() or ParseFile() methods are called; calling it after either of those have been called causes ExpatError to be raised with the code attribute set to errors.XML_ERROR_CANT_CHANGE_FEATURE_ONCE_PARSING.

New in version 2.3.

xmlparser objects have the following attributes:

buffer_size: The size of the buffer used when buffer_text is true. This value cannot be changed at this time. New in version 2.3.

buffer_text: Setting this to true causes the xmlparser object to buffer textual content returned by Expat to avoid multiple calls to the CharacterDataHandler() callback whenever possible. This can improve performance substantially since Expat normally breaks character data into chunks at every line ending. This attribute is false by default, and may be changed at any time. New in version 2.3.

buffer_used: If buffer_text is enabled, the number of bytes stored in the buffer. These bytes represent UTF-8 encoded text. This attribute has no meaningful interpretation when buffer_text is false. New in version 2.3.

ordered_attributes: Setting this attribute to a non-zero integer causes the attributes to be reported as a list rather than a dictionary. The attributes are presented in the order found in the document text. For each attribute, two list entries are presented: the attribute name and the attribute value. (Older versions of this module also used this format.) By default, this attribute is false; it may be changed at any time. New in version 2.1.

returns_unicode: If this attribute is set to a non-zero integer, the handler functions will be passed Unicode strings. If returns_unicode is 0, 8-bit strings containing UTF-8 encoded data will be passed to the handlers. Changed in version 1.6: Can be changed at any time to affect the result type.

specified_attributes: If set to a non-zero integer, the parser will report only those attributes which were specified in the document instance and not those which were derived from attribute declarations. Applications which set this need to be especially careful to use what additional information is available from the declarations as needed to comply with the standards for the behavior of XML processors. By default, this attribute is false; it may be changed at any time. New in version 2.1.

The following attributes contain values relating to the most recent error encountered by an xmlparser object, and will only have correct values once a call to Parse() or ParseFile() has raised a xml.parsers.expat.ExpatError exception.

ErrorByteIndex: Byte index at which an error occurred.

ErrorCode: Numeric code specifying the problem. This value can be passed to the ErrorString() function, or compared to one of the constants defined in the errors object.

ErrorColumnNumber: Column number at which an error occurred.

ErrorLineNumber: Line number at which an error occurred.

The following attributes contain values relating to the current parse location in an xmlparser object. During a callback reporting a parse event they indicate the location of the first of the sequence of characters that generated the event. When called outside of a callback, the position indicated will be just past the last parse event (regardless of whether there was an associated callback). New in version 2.4.

CurrentByteIndex: Current byte index in the parser input.

CurrentColumnNumber: Current column number in the parser input.

CurrentLineNumber: Current line number in the parser input.

Here is the list of handlers that can be set. To set a handler on an xmlparser object o, use o.handlername = func. handlername must be taken from the following list, and func must be a callable object accepting the correct number of arguments. The arguments are all strings, unless otherwise stated.

XmlDeclHandler( version, encoding, standalone): Called when the XML declaration is parsed. The XML declaration is the (optional) declaration of the applicable version of the XML recommendation, the encoding of the document text, and an optional ``standalone'' declaration. version and encoding will be strings of the type dictated by the returns_unicode attribute, and standalone will be 1 if the document is declared standalone, 0 if it is declared not to be standalone, or -1 if the standalone clause was omitted. This is only available with Expat version 1.95.0 or newer. New in version 2.1.

StartDoctypeDeclHandler( doctypeName, systemId, publicId, has_internal_subset): Called when Expat begins parsing the document type declaration (<!DOCTYPE ...). The doctypeName is provided exactly as presented. The systemId and publicId parameters give the system and public identifiers if specified, or None if omitted. has_internal_subset will be true if the document contains and internal document declaration subset. This requires Expat version 1.2 or newer.

EndDoctypeDeclHandler( ): Called when Expat is done parsing the document type delaration. This requires Expat version 1.2 or newer.

ElementDeclHandler( name, model): Called once for each element type declaration. name is the name of the element type, and model is a representation of the content model.

AttlistDeclHandler( elname, attname, type, default, required): Called for each declared attribute for an element type. If an attribute list declaration declares three attributes, this handler is called three times, once for each attribute. elname is the name of the element to which the declaration applies and attname is the name of the attribute declared. The attribute type is a string passed as type; the possible values are 'CDATA', 'ID', 'IDREF', ... default gives the default value for the attribute used when the attribute is not specified by the document instance, or None if there is no default value (#IMPLIED values). If the attribute is required to be given in the document instance, required will be true. This requires Expat version 1.95.0 or newer.

StartElementHandler( name, attributes): Called for the start of every element. name is a string containing the element name, and attributes is a dictionary mapping attribute names to their values.

EndElementHandler( name): Called for the end of every element.

ProcessingInstructionHandler( target, data): Called for every processing instruction.

CharacterDataHandler( data): Called for character data. This will be called for normal character data, CDATA marked content, and ignorable whitespace. Applications which must distinguish these cases can use the StartCdataSectionHandler, EndCdataSectionHandler, and ElementDeclHandler callbacks to collect the required information.

UnparsedEntityDeclHandler( entityName, base, systemId, publicId, notationName): Called for unparsed (NDATA) entity declarations. This is only present for version 1.2 of the Expat library; for more recent versions, use EntityDeclHandler instead. (The underlying function in the Expat library has been declared obsolete.)

EntityDeclHandler( entityName, is_parameter_entity, value, base, systemId, publicId, notationName): Called for all entity declarations. For parameter and internal entities, value will be a string giving the declared contents of the entity; this will be None for external entities. The notationName parameter will be None for parsed entities, and the name of the notation for unparsed entities. is_parameter_entity will be true if the entity is a paremeter entity or false for general entities (most applications only need to be concerned with general entities). This is only available starting with version 1.95.0 of the Expat library. New in version 2.1.

NotationDeclHandler( notationName, base, systemId, publicId): Called for notation declarations. notationName, base, and systemId, and publicId are strings if given. If the public identifier is omitted, publicId will be None.

StartNamespaceDeclHandler( prefix, uri): Called when an element contains a namespace declaration. Namespace declarations are processed before the StartElementHandler is called for the element on which declarations are placed.

EndNamespaceDeclHandler( prefix): Called when the closing tag is reached for an element that contained a namespace declaration. This is called once for each namespace declaration on the element in the reverse of the order for which the StartNamespaceDeclHandler was called to indicate the start of each namespace declaration's scope. Calls to this handler are made after the corresponding EndElementHandler for the end of the element.

CommentHandler( data): Called for comments. data is the text of the comment, excluding the leading `'.

StartCdataSectionHandler( ): Called at the start of a CDATA section. This and StartCdataSectionHandler are needed to be able to identify the syntactical start and end for CDATA sections.

EndCdataSectionHandler( ): Called at the end of a CDATA section.

DefaultHandler( data): Called for any characters in the XML document for which no applicable handler has been specified. This means characters that are part of a construct which could be reported, but for which no handler has been supplied.

DefaultHandlerExpand( data): This is the same as the DefaultHandler, but doesn't inhibit expansion of internal entities. The entity reference will not be passed to the default handler.

NotStandaloneHandler( ): Called if the XML document hasn't been declared as being a standalone document. This happens when there is an external subset or a reference to a parameter entity, but the XML declaration does not set standalone to yes in an XML declaration. If this handler returns 0, then the parser will throw an XML_ERROR_NOT_STANDALONE error. If this handler is not set, no exception is raised by the parser for this condition.

ExternalEntityRefHandler( context, base, systemId, publicId)

Called for references to external entities. base is the current base, as set by a previous call to SetBase(). The public and system identifiers, systemId and publicId, are strings if given; if the public identifier is not given, publicId will be None. The context value is opaque and should only be used as described below.

For external entities to be parsed, this handler must be implemented. It is responsible for creating the sub-parser using ExternalEntityParserCreate(context), initializing it with the appropriate callbacks, and parsing the entity. This handler should return an integer; if it returns 0, the parser will throw an XML_ERROR_EXTERNAL_ENTITY_HANDLING error, otherwise parsing will continue.

If this handler is not provided, external entities are reported by the DefaultHandler callback, if provided.

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