20.9. xml.sax — Support for SAX2 parsers
The xml.sax package provides a number of modules which implement the Simple API for XML (SAX) interface for Python. The package itself provides the SAX exceptions and the convenience functions which will be most used by users of the SAX API.
The convenience functions are:
Create and return a SAX XMLReader object. The first parser found will be used. If parser_list is provided, it must be a sequence of strings which name modules that have a function named create_parser(). Modules listed in parser_list will be used before modules in the default list of parsers.
- xml.sax.parse(filename_or_stream, handler, error_handler=handler.ErrorHandler())
Create a SAX parser and use it to parse a document. The document, passed in as filename_or_stream, can be a filename or a file object. The handler parameter needs to be a SAX ContentHandler instance. If error_handler is given, it must be a SAX ErrorHandler instance; if omitted, SAXParseException will be raised on all errors. There is no return value; all work must be done by the handler passed in.
- xml.sax.parseString(string, handler, error_handler=handler.ErrorHandler())
Similar to parse(), but parses from a buffer string received as a parameter.
A typical SAX application uses three kinds of objects: readers, handlers and input sources. “Reader” in this context is another term for parser, i.e. some piece of code that reads the bytes or characters from the input source, and produces a sequence of events. The events then get distributed to the handler objects, i.e. the reader invokes a method on the handler. A SAX application must therefore obtain a reader object, create or open the input sources, create the handlers, and connect these objects all together. As the final step of preparation, the reader is called to parse the input. During parsing, methods on the handler objects are called based on structural and syntactic events from the input data.
For these objects, only the interfaces are relevant; they are normally not instantiated by the application itself. Since Python does not have an explicit notion of interface, they are formally introduced as classes, but applications may use implementations which do not inherit from the provided classes. The InputSource, Locator, Attributes, AttributesNS, and XMLReader interfaces are defined in the module xml.sax.xmlreader. The handler interfaces are defined in xml.sax.handler. For convenience, InputSource (which is often instantiated directly) and the handler classes are also available from xml.sax. These interfaces are described below.
In addition to these classes, xml.sax provides the following exception classes.
- exception xml.sax.SAXException(msg, exception=None)
Encapsulate an XML error or warning. This class can contain basic error or warning information from either the XML parser or the application: it can be subclassed to provide additional functionality or to add localization. Note that although the handlers defined in the ErrorHandler interface receive instances of this exception, it is not required to actually raise the exception — it is also useful as a container for information.
When instantiated, msg should be a human-readable description of the error. The optional exception parameter, if given, should be None or an exception that was caught by the parsing code and is being passed along as information.
This is the base class for the other SAX exception classes.
- exception xml.sax.SAXParseException(msg, exception, locator)
Subclass of SAXException raised on parse errors. Instances of this class are passed to the methods of the SAX ErrorHandler interface to provide information about the parse error. This class supports the SAX Locator interface as well as the SAXException interface.
- exception xml.sax.SAXNotRecognizedException(msg, exception=None)
- exception xml.sax.SAXNotSupportedException(msg, exception=None)
Subclass of SAXException raised when a SAX XMLReader is asked to enable a feature that is not supported, or to set a property to a value that the implementation does not support. SAX applications and extensions may use this class for similar purposes.
- SAX: The Simple API for XML
- This site is the focal point for the definition of the SAX API. It provides a Java implementation and online documentation. Links to implementations and historical information are also available.
- Module xml.sax.handler
- Definitions of the interfaces for application-provided objects.
- Module xml.sax.saxutils
- Convenience functions for use in SAX applications.
- Module xml.sax.xmlreader
- Definitions of the interfaces for parser-provided objects.
20.9.1. SAXException Objects
The SAXException exception class supports the following methods:
Return a human-readable message describing the error condition.
Return an encapsulated exception object, or None.