382 lines
16 KiB
TeX
382 lines
16 KiB
TeX
\section{\module{xml.sax.handler} ---
|
|
Base classes for SAX handlers}
|
|
|
|
\declaremodule{standard}{xml.sax.handler}
|
|
\modulesynopsis{Base classes for SAX event handlers.}
|
|
\sectionauthor{Martin v. L\"owis}{martin@v.loewis.de}
|
|
\moduleauthor{Lars Marius Garshol}{larsga@garshol.priv.no}
|
|
|
|
\versionadded{2.0}
|
|
|
|
|
|
The SAX API defines four kinds of handlers: content handlers, DTD
|
|
handlers, error handlers, and entity resolvers. Applications normally
|
|
only need to implement those interfaces whose events they are
|
|
interested in; they can implement the interfaces in a single object or
|
|
in multiple objects. Handler implementations should inherit from the
|
|
base classes provided in the module \module{xml.sax}, so that all
|
|
methods get default implementations.
|
|
|
|
\begin{classdesc*}{ContentHandler}
|
|
This is the main callback interface in SAX, and the one most
|
|
important to applications. The order of events in this interface
|
|
mirrors the order of the information in the document.
|
|
\end{classdesc*}
|
|
|
|
\begin{classdesc*}{DTDHandler}
|
|
Handle DTD events.
|
|
|
|
This interface specifies only those DTD events required for basic
|
|
parsing (unparsed entities and attributes).
|
|
\end{classdesc*}
|
|
|
|
\begin{classdesc*}{EntityResolver}
|
|
Basic interface for resolving entities. If you create an object
|
|
implementing this interface, then register the object with your
|
|
Parser, the parser will call the method in your object to resolve all
|
|
external entities.
|
|
\end{classdesc*}
|
|
|
|
\begin{classdesc*}{ErrorHandler}
|
|
Interface used by the parser to present error and warning messages
|
|
to the application. The methods of this object control whether errors
|
|
are immediately converted to exceptions or are handled in some other
|
|
way.
|
|
\end{classdesc*}
|
|
|
|
In addition to these classes, \module{xml.sax.handler} provides
|
|
symbolic constants for the feature and property names.
|
|
|
|
\begin{datadesc}{feature_namespaces}
|
|
Value: \code{"http://xml.org/sax/features/namespaces"}\\
|
|
true: Perform Namespace processing.\\
|
|
false: Optionally do not perform Namespace processing
|
|
(implies namespace-prefixes; default).\\
|
|
access: (parsing) read-only; (not parsing) read/write
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{feature_namespace_prefixes}
|
|
Value: \code{"http://xml.org/sax/features/namespace-prefixes"}\\
|
|
true: Report the original prefixed names and attributes used for Namespace
|
|
declarations.\\
|
|
false: Do not report attributes used for Namespace declarations, and
|
|
optionally do not report original prefixed names (default).\\
|
|
access: (parsing) read-only; (not parsing) read/write
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{feature_string_interning}
|
|
Value: \code{"http://xml.org/sax/features/string-interning"}\\
|
|
true: All element names, prefixes, attribute names, Namespace URIs, and
|
|
local 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
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{feature_validation}
|
|
Value: \code{"http://xml.org/sax/features/validation"}\\
|
|
true: Report all validation errors (implies external-general-entities and
|
|
external-parameter-entities).\\
|
|
false: Do not report validation errors.\\
|
|
access: (parsing) read-only; (not parsing) read/write
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{feature_external_ges}
|
|
Value: \code{"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
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{feature_external_pes}
|
|
Value: \code{"http://xml.org/sax/features/external-parameter-entities"}\\
|
|
true: Include all external parameter entities, including the external
|
|
DTD subset.\\
|
|
false: Do not include any external parameter entities, even the external
|
|
DTD subset.\\
|
|
access: (parsing) read-only; (not parsing) read/write
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{all_features}
|
|
List of all features.
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{property_lexical_handler}
|
|
Value: \code{"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 like comments.\\
|
|
access: read/write
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{property_declaration_handler}
|
|
Value: \code{"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 other
|
|
than notations and unparsed entities.\\
|
|
access: read/write
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{property_dom_node}
|
|
Value: \code{"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 is
|
|
a DOM iterator; when not parsing, the root DOM node for
|
|
iteration.\\
|
|
access: (parsing) read-only; (not parsing) read/write
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{property_xml_string}
|
|
Value: \code{"http://xml.org/sax/properties/xml-string"}\\
|
|
data type: String\\
|
|
description: The literal string of characters that was the source for
|
|
the current event.\\
|
|
access: read-only
|
|
\end{datadesc}
|
|
|
|
\begin{datadesc}{all_properties}
|
|
List of all known property names.
|
|
\end{datadesc}
|
|
|
|
|
|
\subsection{ContentHandler Objects \label{content-handler-objects}}
|
|
|
|
Users are expected to subclass \class{ContentHandler} to support their
|
|
application. The following methods are called by the parser on the
|
|
appropriate events in the input document:
|
|
|
|
\begin{methoddesc}[ContentHandler]{setDocumentLocator}{locator}
|
|
Called by the parser to give the application a locator for locating
|
|
the origin of document events.
|
|
|
|
SAX parsers are strongly encouraged (though not absolutely required)
|
|
to supply a locator: if it does so, it must supply the locator to
|
|
the application by invoking this method before invoking any of the
|
|
other methods in the DocumentHandler interface.
|
|
|
|
The locator allows the application to determine the end position of
|
|
any document-related event, even if the parser is not reporting an
|
|
error. Typically, the application will use this information for
|
|
reporting its own errors (such as character content that does not
|
|
match an application's business rules). The information returned by
|
|
the locator is probably not sufficient for use with a search engine.
|
|
|
|
Note that the locator will return correct information only during
|
|
the invocation of the events in this interface. The application
|
|
should not attempt to use it at any other time.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ContentHandler]{startDocument}{}
|
|
Receive notification of the beginning of a document.
|
|
|
|
The SAX parser will invoke this method only once, before any other
|
|
methods in this interface or in DTDHandler (except for
|
|
\method{setDocumentLocator()}).
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[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 method invoked during the parse. The parser shall not invoke
|
|
this method until it has either abandoned parsing (because of an
|
|
unrecoverable error) or reached the end of input.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ContentHandler]{startPrefixMapping}{prefix, uri}
|
|
Begin the scope of a prefix-URI Namespace mapping.
|
|
|
|
The information from this event is not necessary for normal
|
|
Namespace processing: the SAX XML reader will automatically replace
|
|
prefixes for element and attribute names when the
|
|
\code{feature_namespaces} feature is enabled (the default).
|
|
|
|
%% XXX This is not really the default, is it? MvL
|
|
|
|
There are cases, however, when applications need to use prefixes in
|
|
character data or in attribute values, where they cannot safely be
|
|
expanded automatically; the \method{startPrefixMapping()} and
|
|
\method{endPrefixMapping()} events supply the information to the
|
|
application to expand prefixes in those contexts itself, if
|
|
necessary.
|
|
|
|
Note that \method{startPrefixMapping()} and
|
|
\method{endPrefixMapping()} events are not guaranteed to be properly
|
|
nested relative to each-other: all \method{startPrefixMapping()}
|
|
events will occur before the corresponding \method{startElement()}
|
|
event, and all \method{endPrefixMapping()} events will occur after
|
|
the corresponding \method{endElement()} event, but their order is
|
|
not guaranteed.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ContentHandler]{endPrefixMapping}{prefix}
|
|
End the scope of a prefix-URI mapping.
|
|
|
|
See \method{startPrefixMapping()} for details. This event will
|
|
always occur after the corresponding \method{endElement()} event,
|
|
but the order of \method{endPrefixMapping()} events is not otherwise
|
|
guaranteed.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ContentHandler]{startElement}{name, attrs}
|
|
Signals the start of an element in non-namespace mode.
|
|
|
|
The \var{name} parameter contains the raw XML 1.0 name of the
|
|
element type as a string and the \var{attrs} parameter holds an
|
|
object of the \ulink{\class{Attributes}
|
|
interface}{attributes-objects.html} containing the attributes of the
|
|
element. The object passed as \var{attrs} may be re-used by the
|
|
parser; holding on 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 \method{copy()} method of the \var{attrs} object.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ContentHandler]{endElement}{name}
|
|
Signals the end of an element in non-namespace mode.
|
|
|
|
The \var{name} parameter contains the name of the element type, just
|
|
as with the \method{startElement()} event.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ContentHandler]{startElementNS}{name, qname, attrs}
|
|
Signals the start of an element in namespace mode.
|
|
|
|
The \var{name} parameter contains the name of the element type as a
|
|
\code{(\var{uri}, \var{localname})} tuple, the \var{qname} parameter
|
|
contains the raw XML 1.0 name used in the source document, and the
|
|
\var{attrs} parameter holds an instance of the
|
|
\ulink{\class{AttributesNS} interface}{attributes-ns-objects.html}
|
|
containing the attributes of the element. If no namespace is
|
|
associated with the element, the \var{uri} component of \var{name}
|
|
will be \code{None}. The object passed as \var{attrs} may be
|
|
re-used by the parser; holding on 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 \method{copy()} method of the \var{attrs}
|
|
object.
|
|
|
|
Parsers may set the \var{qname} parameter to \code{None}, unless the
|
|
\code{feature_namespace_prefixes} feature is activated.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ContentHandler]{endElementNS}{name, qname}
|
|
Signals the end of an element in namespace mode.
|
|
|
|
The \var{name} parameter contains the name of the element type, just
|
|
as with the \method{startElementNS()} method, likewise the
|
|
\var{qname} parameter.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ContentHandler]{characters}{content}
|
|
Receive notification of character data.
|
|
|
|
The Parser will call this method to report each chunk of character
|
|
data. SAX parsers may return all contiguous character data in a
|
|
single chunk, or they may split it into several chunks; however, all
|
|
of the characters in any single event must come from the same
|
|
external entity so that the Locator provides useful information.
|
|
|
|
\var{content} may be a Unicode string or a byte string; the
|
|
\code{expat} reader module produces always Unicode strings.
|
|
|
|
\note{The earlier SAX 1 interface provided by the Python
|
|
XML Special Interest Group used a more Java-like interface for this
|
|
method. Since most parsers used from Python did not take advantage
|
|
of the older interface, the simpler signature was chosen to replace
|
|
it. To convert old code to the new interface, use \var{content}
|
|
instead of slicing content with the old \var{offset} and
|
|
\var{length} parameters.}
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ContentHandler]{ignorableWhitespace}{whitespace}
|
|
Receive notification of ignorable whitespace in element content.
|
|
|
|
Validating Parsers must use this method to report each chunk
|
|
of ignorable whitespace (see the W3C XML 1.0 recommendation,
|
|
section 2.10): non-validating parsers may also use this method
|
|
if they are capable of parsing and using content models.
|
|
|
|
SAX parsers may return all contiguous whitespace in a single
|
|
chunk, or they may split it into several chunks; however, all
|
|
of the characters in any single event must come from the same
|
|
external entity, so that the Locator provides useful
|
|
information.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[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 document element.
|
|
|
|
A SAX parser should never report an XML declaration (XML 1.0,
|
|
section 2.8) or a text declaration (XML 1.0, section 4.3.1) using
|
|
this method.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ContentHandler]{skippedEntity}{name}
|
|
Receive notification of a skipped entity.
|
|
|
|
The Parser will invoke this method once for each entity
|
|
skipped. Non-validating processors may skip entities if they have
|
|
not seen the declarations (because, for example, the entity was
|
|
declared in an external DTD subset). All processors may skip
|
|
external entities, depending on the values of the
|
|
\code{feature_external_ges} and the
|
|
\code{feature_external_pes} properties.
|
|
\end{methoddesc}
|
|
|
|
|
|
\subsection{DTDHandler Objects \label{dtd-handler-objects}}
|
|
|
|
\class{DTDHandler} instances provide the following methods:
|
|
|
|
\begin{methoddesc}[DTDHandler]{notationDecl}{name, publicId, systemId}
|
|
Handle a notation declaration event.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[DTDHandler]{unparsedEntityDecl}{name, publicId,
|
|
systemId, ndata}
|
|
Handle an unparsed entity declaration event.
|
|
\end{methoddesc}
|
|
|
|
|
|
\subsection{EntityResolver Objects \label{entity-resolver-objects}}
|
|
|
|
\begin{methoddesc}[EntityResolver]{resolveEntity}{publicId, systemId}
|
|
Resolve the system identifier of an entity and return either the
|
|
system identifier to read from as a string, or an InputSource to
|
|
read from. The default implementation returns \var{systemId}.
|
|
\end{methoddesc}
|
|
|
|
|
|
\subsection{ErrorHandler Objects \label{sax-error-handler}}
|
|
|
|
Objects with this interface are used to receive error and warning
|
|
information from the \class{XMLReader}. If you create an object that
|
|
implements this interface, then register the object with your
|
|
\class{XMLReader}, the parser will call the methods in your object to
|
|
report all warnings and errors. There are three levels of errors
|
|
available: warnings, (possibly) recoverable errors, and unrecoverable
|
|
errors. All methods take a \exception{SAXParseException} as the only
|
|
parameter. Errors and warnings may be converted to an exception by
|
|
raising the passed-in exception object.
|
|
|
|
\begin{methoddesc}[ErrorHandler]{error}{exception}
|
|
Called when the parser encounters a recoverable error. If this method
|
|
does not raise an exception, parsing may continue, but further document
|
|
information should not be expected by the application. Allowing the
|
|
parser to continue may allow additional errors to be discovered in the
|
|
input document.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ErrorHandler]{fatalError}{exception}
|
|
Called when the parser encounters an error it cannot recover from;
|
|
parsing is expected to terminate when this method returns.
|
|
\end{methoddesc}
|
|
|
|
\begin{methoddesc}[ErrorHandler]{warning}{exception}
|
|
Called when the parser presents minor warning information to the
|
|
application. Parsing is expected to continue when this method returns,
|
|
and document information will continue to be passed to the application.
|
|
Raising an exception in this method will cause parsing to end.
|
|
\end{methoddesc}
|