\section{\module{xml.parsers.expat} ---         Fast XML parsing using Expat} % Markup notes:%% Many of the attributes of the XMLParser objects are callbacks.% Since signature information must be presented, these are described% using the methoddesc environment.  Since they are attributes which% are set by client code, in-text references to these attributes% should be marked using the \member macro and should not include the% parentheses used when marking functions and methods. \declaremodule{standard}{xml.parsers.expat}\modulesynopsis{An interface to the Expat non-validating XML parser.}\moduleauthor{Paul Prescod}{paul@prescod.net} \versionadded{2.0} The \module{xml.parsers.expat} module is a Python interface to theExpat\index{Expat} non-validating XML parser.The module provides a single extension type, \class{xmlparser}, thatrepresents the current state of an XML parser.  After an\class{xmlparser} object has been created, various attributes of the object can be set to handler functions.  When an XML document is then fed tothe parser, the handler functions are called for the character dataand markup in the XML document. This module uses the \module{pyexpat}\refbimodindex{pyexpat} module toprovide access to the Expat parser.  Direct use of the\module{pyexpat} module is deprecated. This module provides one exception and one type object: \begin{excdesc}{ExpatError}  The exception raised when Expat reports an error.  See section  \ref{expaterror-objects}, ``ExpatError Exceptions,'' for more  information on interpreting Expat errors.\end{excdesc} \begin{excdesc}{error}  Alias for \exception{ExpatError}.\end{excdesc} \begin{datadesc}{XMLParserType}  The type of the return values from the \function{ParserCreate()}  function.\end{datadesc}  The \module{xml.parsers.expat} module contains two functions: \begin{funcdesc}{ErrorString}{errno}Returns an explanatory string for a given error number \var{errno}.\end{funcdesc} \begin{funcdesc}{ParserCreate}{\optional{encoding\optional{,                               namespace_separator}}}Creates and returns a new \class{xmlparser} object.  \var{encoding}, if specified, must be a string naming the encoding used by the XML data.  Expat doesn't support as many encodings asPython does, and its repertoire of encodings can't be extended; itsupports UTF-8, UTF-16, ISO-8859-1 (Latin1), and ASCII.  If\var{encoding} is given it will override the implicit or explicitencoding of the document. Expat can optionally do XML namespace processing for you, enabled byproviding a value for \var{namespace_separator}.  The value must be aone-character string; a \exception{ValueError} will be raised if thestring has an illegal length (\code{None} is considered the same asomission).  When namespace processing is enabled, element type namesand attribute names that belong to a namespace will be expanded.  Theelement name passed to the element handlers\member{StartElementHandler} and \member{EndElementHandler}will be the concatenation of the namespace URI, the namespaceseparator character, and the local part of the name.  If the namespaceseparator is a zero byte (\code{chr(0)}) then the namespace URI andthe local part will be concatenated without any separator. For example, if \var{namespace_separator} is set to a space character(\character{ }) and the following document is parsed: \begin{verbatim}<?xml version="1.0"?><root xmlns    = "http://default-namespace.org/"      xmlns:py = "http://www.python.org/ns/">  <py:elem1 />  <elem2 xmlns="" /></root>\end{verbatim} \member{StartElementHandler} will receive the following stringsfor each element: \begin{verbatim}http://default-namespace.org/ roothttp://www.python.org/ns/ elem1elem2\end{verbatim}\end{funcdesc}  \begin{seealso}  \seetitle[http://www.libexpat.org/]{The Expat XML Parser}           {Home page of the Expat project.}\end{seealso}  \subsection{XMLParser Objects \label{xmlparser-objects}} \class{xmlparser} objects have the following methods: \begin{methoddesc}[xmlparser]{Parse}{data\optional{, isfinal}}Parses the contents of the string \var{data}, calling the appropriatehandler functions to process the parsed data.  \var{isfinal} must betrue on the final call to this method.  \var{data} can be the emptystring at any time.\end{methoddesc} \begin{methoddesc}[xmlparser]{ParseFile}{file}Parse XML data reading from the object \var{file}.  \var{file} onlyneeds to provide the \method{read(\var{nbytes})} method, returning theempty string when there's no more data.\end{methoddesc} \begin{methoddesc}[xmlparser]{SetBase}{base}Sets the base to be used for resolving relative URIs in systemidentifiers in declarations.  Resolving relative identifiers is leftto the application: this value will be passed through as the\var{base} argument to the \function{ExternalEntityRefHandler},\function{NotationDeclHandler}, and\function{UnparsedEntityDeclHandler} functions.\end{methoddesc} \begin{methoddesc}[xmlparser]{GetBase}{}Returns a string containing the base set by a previous call to\method{SetBase()}, or \code{None} if \method{SetBase()} hasn't been called.\end{methoddesc} \begin{methoddesc}[xmlparser]{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\code{None}.\versionadded{2.1}\end{methoddesc} \begin{methoddesc}[xmlparser]{ExternalEntityParserCreate}{context\optional{,                                                          encoding}}Create a ``child'' parser which can be used to parse an externalparsed entity referred to by content parsed by the parent parser.  The\var{context} parameter should be the string passed to the\method{ExternalEntityRefHandler()} handler function, described below.The child parser is created with the \member{ordered_attributes},\member{returns_unicode} and \member{specified_attributes} set to thevalues of this parser.\end{methoddesc} \begin{methoddesc}[xmlparser]{UseForeignDTD}{\optional{flag}}Calling this with a true value for \var{flag} (the default) will causeExpat to call the \member{ExternalEntityRefHandler} with\constant{None} for all arguments to allow an alternate DTD to beloaded.  If the document does not contain a document type declaration,the \member{ExternalEntityRefHandler} will still be called, but the\member{StartDoctypeDeclHandler} and \member{EndDoctypeDeclHandler}will not be called. Passing a false value for \var{flag} will cancel a previous call thatpassed a true value, but otherwise has no effect. This method can only be called before the \method{Parse()} or\method{ParseFile()} methods are called; calling it after either ofthose have been called causes \exception{ExpatError} to be raised withthe \member{code} attribute set to\constant{errors.XML_ERROR_CANT_CHANGE_FEATURE_ONCE_PARSING}. \versionadded{2.3}\end{methoddesc}  \class{xmlparser} objects have the following attributes: \begin{memberdesc}[xmlparser]{buffer_size}The size of the buffer used when \member{buffer_text} is true.  Thisvalue cannot be changed at this time.\versionadded{2.3}\end{memberdesc} \begin{memberdesc}[xmlparser]{buffer_text}Setting this to true causes the \class{xmlparser} object to buffertextual content returned by Expat to avoid multiple calls to the\method{CharacterDataHandler()} callback whenever possible.  This canimprove performance substantially since Expat normally breakscharacter data into chunks at every line ending.  This attribute isfalse by default, and may be changed at any time.\versionadded{2.3}\end{memberdesc} \begin{memberdesc}[xmlparser]{buffer_used}If \member{buffer_text} is enabled, the number of bytes stored in thebuffer.  These bytes represent UTF-8 encoded text.  This attribute hasno meaningful interpretation when \member{buffer_text} is false.\versionadded{2.3}\end{memberdesc} \begin{memberdesc}[xmlparser]{ordered_attributes}Setting this attribute to a non-zero integer causes the attributes tobe reported as a list rather than a dictionary.  The attributes arepresented in the order found in the document text.  For eachattribute, two list entries are presented: the attribute name and theattribute value.  (Older versions of this module also used thisformat.)  By default, this attribute is false; it may be changed atany time.\versionadded{2.1}\end{memberdesc} \begin{memberdesc}[xmlparser]{returns_unicode} If this attribute is set to a non-zero integer, the handler functionswill be passed Unicode strings.  If \member{returns_unicode} is\constant{False}, 8-bit strings containing UTF-8 encoded data will bepassed to the handlers.  This is \constant{True} by default whenPython is built with Unicode support.\versionchanged[Can be changed at any time to affect the result  type]{1.6}\end{memberdesc} \begin{memberdesc}[xmlparser]{specified_attributes}If set to a non-zero integer, the parser will report only thoseattributes which were specified in the document instance and not thosewhich were derived from attribute declarations.  Applications whichset this need to be especially careful to use what additionalinformation is available from the declarations as needed to complywith the standards for the behavior of XML processors.  By default,this attribute is false; it may be changed at any time.\versionadded{2.1}\end{memberdesc} The following attributes contain values relating to the most recenterror encountered by an \class{xmlparser} object, and will only havecorrect values once a call to \method{Parse()} or \method{ParseFile()}has raised a \exception{xml.parsers.expat.ExpatError} exception. \begin{memberdesc}[xmlparser]{ErrorByteIndex} Byte index at which an error occurred.\end{memberdesc}  \begin{memberdesc}[xmlparser]{ErrorCode} Numeric code specifying the problem.  This value can be passed to the\function{ErrorString()} function, or compared to one of the constantsdefined in the \code{errors} object.\end{memberdesc} \begin{memberdesc}[xmlparser]{ErrorColumnNumber} Column number at which an error occurred.\end{memberdesc} \begin{memberdesc}[xmlparser]{ErrorLineNumber}Line number at which an error occurred.\end{memberdesc} The following attributes contain values relating to the current parselocation in an \class{xmlparser} object.  During a callback reportinga parse event they indicate the location of the first of the sequenceof characters that generated the event.  When called outside of acallback, the position indicated will be just past the last parseevent (regardless of whether there was an associated callback).\versionadded{2.4} \begin{memberdesc}[xmlparser]{CurrentByteIndex} Current byte index in the parser input.\end{memberdesc}  \begin{memberdesc}[xmlparser]{CurrentColumnNumber} Current column number in the parser input.\end{memberdesc} \begin{memberdesc}[xmlparser]{CurrentLineNumber}Current line number in the parser input.\end{memberdesc} Here is the list of handlers that can be set.  To set a handler on an\class{xmlparser} object \var{o}, use\code{\var{o}.\var{handlername} = \var{func}}.  \var{handlername} mustbe taken from the following list, and \var{func} must be a callableobject accepting the correct number of arguments.  The arguments areall strings, unless otherwise stated. \begin{methoddesc}[xmlparser]{XmlDeclHandler}{version, encoding, standalone}Called when the XML declaration is parsed.  The XML declaration is the(optional) declaration of the applicable version of the XMLrecommendation, the encoding of the document text, and an optional``standalone'' declaration.  \var{version} and \var{encoding} will bestrings of the type dictated by the \member{returns_unicode}attribute, and \var{standalone} will be \code{1} if the document isdeclared standalone, \code{0} if it is declared not to be standalone,or \code{-1} if the standalone clause was omitted.This is only available with Expat version 1.95.0 or newer.\versionadded{2.1}\end{methoddesc} \begin{methoddesc}[xmlparser]{StartDoctypeDeclHandler}{doctypeName,                                                       systemId, publicId,                                                       has_internal_subset}Called when Expat begins parsing the document type declaration(\code{<!DOCTYPE \ldots}).  The \var{doctypeName} is provided exactlyas presented.  The \var{systemId} and \var{publicId} parameters givethe system and public identifiers if specified, or \code{None} ifomitted.  \var{has_internal_subset} will be true if the documentcontains and internal document declaration subset.This requires Expat version 1.2 or newer.\end{methoddesc} \begin{methoddesc}[xmlparser]{EndDoctypeDeclHandler}{}Called when Expat is done parsing the document type declaration.This requires Expat version 1.2 or newer.\end{methoddesc} \begin{methoddesc}[xmlparser]{ElementDeclHandler}{name, model}Called once for each element type declaration.  \var{name} is the nameof the element type, and \var{model} is a representation of thecontent model.\end{methoddesc} \begin{methoddesc}[xmlparser]{AttlistDeclHandler}{elname, attname,                                                  type, default, required}Called for each declared attribute for an element type.  If anattribute list declaration declares three attributes, this handler iscalled three times, once for each attribute.  \var{elname} is the nameof the element to which the declaration applies and \var{attname} isthe name of the attribute declared.  The attribute type is a stringpassed as \var{type}; the possible values are \code{'CDATA'},\code{'ID'}, \code{'IDREF'}, ...\var{default} gives the default value for the attribute used when theattribute is not specified by the document instance, or \code{None} ifthere is no default value (\code{\#IMPLIED} values).  If the attributeis required to be given in the document instance, \var{required} willbe true.This requires Expat version 1.95.0 or newer.\end{methoddesc} \begin{methoddesc}[xmlparser]{StartElementHandler}{name, attributes}Called for the start of every element.  \var{name} is a stringcontaining the element name, and \var{attributes} is a dictionarymapping attribute names to their values.\end{methoddesc} \begin{methoddesc}[xmlparser]{EndElementHandler}{name}Called for the end of every element.\end{methoddesc} \begin{methoddesc}[xmlparser]{ProcessingInstructionHandler}{target, data}Called for every processing instruction.\end{methoddesc} \begin{methoddesc}[xmlparser]{CharacterDataHandler}{data}Called for character data.  This will be called for normal characterdata, CDATA marked content, and ignorable whitespace.  Applicationswhich must distinguish these cases can use the\member{StartCdataSectionHandler}, \member{EndCdataSectionHandler},and \member{ElementDeclHandler} callbacks to collect the requiredinformation.\end{methoddesc} \begin{methoddesc}[xmlparser]{UnparsedEntityDeclHandler}{entityName, base,                                                         systemId, publicId,                                                         notationName}Called for unparsed (NDATA) entity declarations.  This is only presentfor version 1.2 of the Expat library; for more recent versions, use\member{EntityDeclHandler} instead.  (The underlying function in theExpat library has been declared obsolete.)\end{methoddesc} \begin{methoddesc}[xmlparser]{EntityDeclHandler}{entityName,                                                 is_parameter_entity, value,                                                 base, systemId,                                                 publicId,                                                 notationName}Called for all entity declarations.  For parameter and internalentities, \var{value} will be a string giving the declared contentsof the entity; this will be \code{None} for external entities.  The\var{notationName} parameter will be \code{None} for parsed entities,and the name of the notation for unparsed entities.\var{is_parameter_entity} will be true if the entity is a parameterentity or false for general entities (most applications only need tobe concerned with general entities).This is only available starting with version 1.95.0 of the Expatlibrary.\versionadded{2.1}\end{methoddesc} \begin{methoddesc}[xmlparser]{NotationDeclHandler}{notationName, base,                                                   systemId, publicId}Called for notation declarations.  \var{notationName}, \var{base}, and\var{systemId}, and \var{publicId} are strings if given.  If thepublic identifier is omitted, \var{publicId} will be \code{None}.\end{methoddesc} \begin{methoddesc}[xmlparser]{StartNamespaceDeclHandler}{prefix, uri}Called when an element contains a namespace declaration.  Namespacedeclarations are processed before the \member{StartElementHandler} iscalled for the element on which declarations are placed.\end{methoddesc} \begin{methoddesc}[xmlparser]{EndNamespaceDeclHandler}{prefix}Called when the closing tag is reached for an element that contained a namespace declaration.  This is called once for eachnamespace declaration on the element in the reverse of the order forwhich the \member{StartNamespaceDeclHandler} was called to indicatethe start of each namespace declaration's scope.  Calls to thishandler are made after the corresponding \member{EndElementHandler}for the end of the element.\end{methoddesc} \begin{methoddesc}[xmlparser]{CommentHandler}{data}Called for comments.  \var{data} is the text of the comment, excludingthe leading `\code{<!-}\code{-}' and trailing `\code{-}\code{->}'.\end{methoddesc} \begin{methoddesc}[xmlparser]{StartCdataSectionHandler}{}Called at the start of a CDATA section.  This and\member{EndCdataSectionHandler} are needed to be able to identifythe syntactical start and end for CDATA sections.\end{methoddesc} \begin{methoddesc}[xmlparser]{EndCdataSectionHandler}{}Called at the end of a CDATA section.\end{methoddesc} \begin{methoddesc}[xmlparser]{DefaultHandler}{data}Called for any characters in the XML document forwhich no applicable handler has been specified.  This meanscharacters that are part of a construct which could be reported, butfor which no handler has been supplied. \end{methoddesc} \begin{methoddesc}[xmlparser]{DefaultHandlerExpand}{data}This is the same as the \function{DefaultHandler}, but doesn't inhibit expansion of internal entities.The entity reference will not be passed to the default handler.\end{methoddesc} \begin{methoddesc}[xmlparser]{NotStandaloneHandler}{} Called if theXML document hasn't been declared as being a standalone document.This happens when there is an external subset or a reference to aparameter entity, but the XML declaration does not set standalone to\code{yes} in an XML declaration.  If this handler returns \code{0},then the parser will throw an \constant{XML_ERROR_NOT_STANDALONE}error.  If this handler is not set, no exception is raised by theparser for this condition.\end{methoddesc} \begin{methoddesc}[xmlparser]{ExternalEntityRefHandler}{context, base,                                                        systemId, publicId}Called for references to external entities.  \var{base} is the currentbase, as set by a previous call to \method{SetBase()}.  The public andsystem identifiers, \var{systemId} and \var{publicId}, are strings ifgiven; if the public identifier is not given, \var{publicId} will be\code{None}.  The \var{context} value is opaque and should only beused as described below. For external entities to be parsed, this handler must be implemented.It is responsible for creating the sub-parser using\code{ExternalEntityParserCreate(\var{context})}, initializing it withthe appropriate callbacks, and parsing the entity.  This handlershould return an integer; if it returns \code{0}, the parser willthrow an \constant{XML_ERROR_EXTERNAL_ENTITY_HANDLING} error,otherwise parsing will continue. If this handler is not provided, external entities are reported by the\member{DefaultHandler} callback, if provided.\end{methoddesc}  \subsection{ExpatError Exceptions \label{expaterror-objects}}\sectionauthor{Fred L. Drake, Jr.}{fdrake@acm.org} \exception{ExpatError} exceptions have a number of interestingattributes: \begin{memberdesc}[ExpatError]{code}  Expat's internal error number for the specific error.  This will  match one of the constants defined in the \code{errors} object from  this module.  \versionadded{2.1}\end{memberdesc} \begin{memberdesc}[ExpatError]{lineno}  Line number on which the error was detected.  The first line is  numbered \code{1}.  \versionadded{2.1}\end{memberdesc} \begin{memberdesc}[ExpatError]{offset}  Character offset into the line where the error occurred.  The first  column is numbered \code{0}.  \versionadded{2.1}\end{memberdesc}  \subsection{Example \label{expat-example}}

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