xml.sax.handler —- Base classes for SAX handlers

Source code:Lib/xml/sax/handler.py

The SAX API defines four kinds of handlers: content handlers, DTD handlers,error handlers, and entity resolvers. Applications normally only need toimplement those interfaces whose events they are interested in; they canimplement the interfaces in a single object or in multiple objects. Handlerimplementations should inherit from the base classes provided in the modulexml.sax.handler, so that all methods get default implementations.

• class xml.sax.handler.ContentHandler

• This is the main callback interface in SAX, and the one most important toapplications. The order of events in this interface mirrors the order of theinformation in the document.

• class xml.sax.handler.DTDHandler

• Handle DTD events.

This interface specifies only those DTD events required for basic parsing(unparsed entities and attributes).

• class xml.sax.handler.EntityResolver

• Basic interface for resolving entities. If you create an object implementingthis interface, then register the object with your Parser, the parser will callthe method in your object to resolve all external entities.

• class xml.sax.handler.ErrorHandler

• Interface used by the parser to present error and warning messages to theapplication. The methods of this object control whether errors are immediatelyconverted to exceptions or are handled in some other way.

In addition to these classes, xml.sax.handler provides symbolic constantsfor the feature and property names.

• xml.sax.handler.feature_namespaces

value: "http://xml.org/sax/features/namespaces"

true: Perform Namespace processing.

false: Optionally do not perform Namespace processing (impliesnamespace-prefixes; default).

access: (parsing) read-only; (not parsing) read/write

• xml.sax.handler.feature_namespace_prefixes

value: "http://xml.org/sax/features/namespace-prefixes"

true: Report the original prefixed names and attributes used for Namespacedeclarations.

false: Do not report attributes used for Namespace declarations, andoptionally do not report original prefixed names (default).

access: (parsing) read-only; (not parsing) read/write

• xml.sax.handler.feature_string_interning

value: "http://xml.org/sax/features/string-interning"

true: All element names, prefixes, attribute names, Namespace URIs, andlocal names are interned using the built-in intern function.

false: Names are not necessarily interned, although they may be (default).

access: (parsing) read-only; (not parsing) read/write

• xml.sax.handler.feature_validation

value: "http://xml.org/sax/features/validation"

true: Report all validation errors (implies external-general-entities andexternal-parameter-entities).

false: Do not report validation errors.

access: (parsing) read-only; (not parsing) read/write

• xml.sax.handler.feature_external_ges

value: "http://xml.org/sax/features/external-general-entities"

true: Include all external general (text) entities.

false: Do not include external general entities.

access: (parsing) read-only; (not parsing) read/write

• xml.sax.handler.feature_external_pes

value: "http://xml.org/sax/features/external-parameter-entities"

true: Include all external parameter entities, including the external DTDsubset.

false: Do not include any external parameter entities, even the externalDTD subset.

access: (parsing) read-only; (not parsing) read/write

• xml.sax.handler.all_features

• List of all features.

• xml.sax.handler.property_lexical_handler

value: "http://xml.org/sax/properties/lexical-handler"

data type: xml.sax.sax2lib.LexicalHandler (not supported in Python 2)

description: An optional extension handler for lexical events likecomments.

access: read/write

• xml.sax.handler.property_declaration_handler

value: "http://xml.org/sax/properties/declaration-handler"

data type: xml.sax.sax2lib.DeclHandler (not supported in Python 2)

description: An optional extension handler for DTD-related events otherthan notations and unparsed entities.

access: read/write

• xml.sax.handler.property_dom_node

value: "http://xml.org/sax/properties/dom-node"

data type: org.w3c.dom.Node (not supported in Python 2)

description: When parsing, the current DOM node being visited if this isa DOM iterator; when not parsing, the root DOM node for iteration.

access: (parsing) read-only; (not parsing) read/write

• xml.sax.handler.property_xml_string

value: "http://xml.org/sax/properties/xml-string"

data type: String

description: The literal string of characters that was the source for thecurrent event.

access: read-only

• xml.sax.handler.all_properties
• List of all known property names.

ContentHandler 对象

Users are expected to subclass ContentHandler to support theirapplication. The following methods are called by the parser on the appropriateevents in the input document:

• ContentHandler.setDocumentLocator(locator)
• Called by the parser to give the application a locator for locating the originof document events.

SAX parsers are strongly encouraged (though not absolutely required) to supply alocator: if it does so, it must supply the locator to the application byinvoking this method before invoking any of the other methods in theDocumentHandler interface.

The locator allows the application to determine the end position of anydocument-related event, even if the parser is not reporting an error. Typically,the application will use this information for reporting its own errors (such ascharacter content that does not match an application's business rules). Theinformation returned by the locator is probably not sufficient for use with asearch engine.

Note that the locator will return correct information only during the invocationof the events in this interface. The application should not attempt to use it atany other time.

• ContentHandler.startDocument()
• Receive notification of the beginning of a document.

The SAX parser will invoke this method only once, before any other methods inthis interface or in DTDHandler (except for setDocumentLocator()).

• ContentHandler.endDocument()
• Receive notification of the end of a document.

The SAX parser will invoke this method only once, and it will be the last methodinvoked during the parse. The parser shall not invoke this method until it haseither abandoned parsing (because of an unrecoverable error) or reached the endof input.

• ContentHandler.startPrefixMapping(prefix, uri)
• Begin the scope of a prefix-URI Namespace mapping.

The information from this event is not necessary for normal Namespaceprocessing: the SAX XML reader will automatically replace prefixes for elementand attribute names when the feature_namespaces feature is enabled (thedefault).

There are cases, however, when applications need to use prefixes in characterdata or in attribute values, where they cannot safely be expanded automatically;the startPrefixMapping() and endPrefixMapping() events supply theinformation to the application to expand prefixes in those contexts itself, ifnecessary.

Note that startPrefixMapping() and endPrefixMapping() events are notguaranteed to be properly nested relative to each-other: allstartPrefixMapping() events will occur before the correspondingstartElement() event, and all endPrefixMapping() events will occurafter the corresponding endElement() event, but their order is notguaranteed.

• ContentHandler.endPrefixMapping(prefix)
• End the scope of a prefix-URI mapping.

See startPrefixMapping() for details. This event will always occur afterthe corresponding endElement() event, but the order ofendPrefixMapping() events is not otherwise guaranteed.

• ContentHandler.startElement(name, attrs)
• Signals the start of an element in non-namespace mode.

The name parameter contains the raw XML 1.0 name of the element type as astring and the attrs parameter holds an object of theAttributesinterface (see The Attributes Interface) containing the attributes ofthe element. The object passed as attrs may be re-used by the parser; holdingon to a reference to it is not a reliable way to keep a copy of the attributes.To keep a copy of the attributes, use the copy() method of the _attrs_object.

• ContentHandler.endElement(name)
• Signals the end of an element in non-namespace mode.

The name parameter contains the name of the element type, just as with thestartElement() event.

• ContentHandler.startElementNS(name, qname, attrs)
• Signals the start of an element in namespace mode.

The name parameter contains the name of the element type as a (uri,localname) tuple, the qname parameter contains the raw XML 1.0 name used inthe source document, and the attrs parameter holds an instance of theAttributesNS interface (seeThe AttributesNS Interface)containing the attributes of the element. If no namespace is associated withthe element, the uri component of name will be None. The object passedas attrs may be re-used by the parser; holding on to a reference to it is nota reliable way to keep a copy of the attributes. To keep a copy of theattributes, use the copy() method of the attrs object.

Parsers may set the qname parameter to None, unless thefeature_namespace_prefixes feature is activated.

• ContentHandler.endElementNS(name, qname)
• Signals the end of an element in namespace mode.

The name parameter contains the name of the element type, just as with thestartElementNS() method, likewise the qname parameter.

• ContentHandler.characters(content)
• Receive notification of character data.

The Parser will call this method to report each chunk of character data. SAXparsers may return all contiguous character data in a single chunk, or they maysplit it into several chunks; however, all of the characters in any single eventmust come from the same external entity so that the Locator provides usefulinformation.

content may be a string or bytes instance; the expat reader modulealways produces strings.

注解

The earlier SAX 1 interface provided by the Python XML Special Interest Groupused a more Java-like interface for this method. Since most parsers used fromPython did not take advantage of the older interface, the simpler signature waschosen to replace it. To convert old code to the new interface, use content_instead of slicing content with the old _offset and length parameters.

• ContentHandler.ignorableWhitespace(whitespace)
• Receive notification of ignorable whitespace in element content.

Validating Parsers must use this method to report each chunk of ignorablewhitespace (see the W3C XML 1.0 recommendation, section 2.10): non-validatingparsers may also use this method if they are capable of parsing and usingcontent models.

SAX parsers may return all contiguous whitespace in a single chunk, or they maysplit it into several chunks; however, all of the characters in any single eventmust come from the same external entity, so that the Locator provides usefulinformation.

• ContentHandler.processingInstruction(target, data)
• Receive notification of a processing instruction.

The Parser will invoke this method once for each processing instruction found:note that processing instructions may occur before or after the main documentelement.

A SAX parser should never report an XML declaration (XML 1.0, section 2.8) or atext declaration (XML 1.0, section 4.3.1) using this method.

• ContentHandler.skippedEntity(name)
• Receive notification of a skipped entity.

The Parser will invoke this method once for each entity skipped. Non-validatingprocessors may skip entities if they have not seen the declarations (because,for example, the entity was declared in an external DTD subset). All processorsmay skip external entities, depending on the values of thefeature_external_ges and the feature_external_pes properties.

DTDHandler 对象

DTDHandler instances provide the following methods:

• DTDHandler.notationDecl(name, publicId, systemId)

• Handle a notation declaration event.

• DTDHandler.unparsedEntityDecl(name, publicId, systemId, ndata)

• Handle an unparsed entity declaration event.

EntityResolver 对象

• EntityResolver.resolveEntity(publicId, systemId)
• Resolve the system identifier of an entity and return either the systemidentifier to read from as a string, or an InputSource to read from. The defaultimplementation returns systemId.

ErrorHandler 对象

Objects with this interface are used to receive error and warning informationfrom the XMLReader. If you create an object thatimplements this interface, then register the object with yourXMLReader, the parserwill call the methods in your object to report all warnings and errors. Thereare three levels of errors available: warnings, (possibly) recoverable errors,and unrecoverable errors. All methods take a SAXParseException as theonly parameter. Errors and warnings may be converted to an exception by raisingthe passed-in exception object.

• ErrorHandler.error(exception)

• Called when the parser encounters a recoverable error. If this method does notraise an exception, parsing may continue, but further document informationshould not be expected by the application. Allowing the parser to continue mayallow additional errors to be discovered in the input document.

• ErrorHandler.fatalError(exception)

• Called when the parser encounters an error it cannot recover from; parsing isexpected to terminate when this method returns.

• ErrorHandler.warning(exception)

• Called when the parser presents minor warning information to the application.Parsing is expected to continue when this method returns, and documentinformation will continue to be passed to the application. Raising an exceptionin this method will cause parsing to end.