# 12.3 `xmllib` -- A parser for XML documents

Changed in version 1.5.2.

This module defines a class `XMLParser` which serves as the basis for parsing text files formatted in XML (Extensible Markup Language).

`XMLParser` ()
  The `XMLParser` class must be instantiated without arguments.

This class provides the following interface methods and instance variables:

`attributes`
  A mapping of element names to mappings. The latter mapping maps attribute names that are valid for the element to the default value of the attribute, or if there is no default to `None`. The default value is the empty dictionary. This variable is meant to be overridden, not extended since the default is shared by all instances of `XMLParser`.

`elements`
  A mapping of element names to tuples. The tuples contain a function for handling the start and end tag respectively of the element, or `None` if the method `unknown_starttag()` or `unknown_endtag()` is to be called. The default value is the empty dictionary. This variable is meant to be overridden, not extended since the default is shared by all instances of `XMLParser`.

`entitydefs`
  A mapping of entitynames to their values. The default value contains definitions for `'lt'`, `'gt'`, `'amp'`, `'quot'`, and `'apos'`.

`reset` ()
  Reset the instance. Loses all unprocessed data. This is called implicitly at the instantiation time.

`setnomoretags` ()
  Stop processing tags. Treat all following input as literal input (CDATA).

`setliteral` ()
  Enter literal mode (CDATA mode). This mode is automatically exited when the close tag matching the last unclosed open tag is encountered.

`feed` (data)
  Feed some text to the parser. It is processed insofar as it consists of complete tags; incomplete data is buffered until more data is fed or `close()` is called.

`close` ()
  Force processing of all buffered data as if it were followed by an end-of-file mark. This method may be redefined by a derived class to define additional processing at the end of the input, but the redefined version should always call `close()`.

`translate_references` (data)
  Translate all entity and character references in data and return the translated string.

`handle_xml` (encoding, standalone)
  This method is called when the "`<?xml ...?>`" tag is processed. The arguments are the values of the encoding and standalone attributes in the tag. Both encoding and standalone are optional. The values passed to `handle_xml()` default to `None` and the string `'no'` respectively.

`handle_doctype` (tag, data)
  This method is called when the "`<!DOCTYPE...>`" tag is processed. The arguments are the name of the root element and the uninterpreted contents of the tag, starting after the white space after the name of the root element.

`handle_starttag` (tag, method, attributes)
  This method is called to handle start tags for which a start tag handler is defined in the instance variable `elements`. The tag argument is the name of the tag, and the method argument is the function (method) which should be used to support semantic interpretation of the start tag. The attributes argument is a dictionary of attributes, the key being the name and the value being the value of the attribute found inside the tag's `<>` brackets. Character and entity references in the value have been interpreted. For instance, for the start tag `<A HREF="http://www.cwi.nl/">`, this method would be called as `handle_starttag('A', self.elements['A'][0], {'HREF': 'http://www.cwi.nl/'})`. The base implementation simply calls method with attributes as the only argument.

`handle_endtag` (tag, method)
  This method is called to handle endtags for which an end tag handler is defined in the instance variable `elements`. The tag argument is the name of the tag, and the method argument is the function (method) which should be used to support semantic interpretation of the end tag. For instance, for the endtag `</A>`, this method would be called as `handle_endtag('A', self.elements['A'][1])`. The base implementation simply calls method.

`handle_data` (data)
  This method is called to process arbitrary data. It is intended to be overridden by a derived class; the base class implementation does nothing.

`handle_charref` (ref)
  This method is called to process a character reference of the form "`&#ref;`". ref can either be a decimal number, or a hexadecimal number when preceded by an "`x`". In the base implementation, ref must be a number in the range 0-255. It translates the character to ASCII and calls the method `handle_data()` with the character as argument. If ref is invalid or out of range, the method `unknown_charref(ref)` is called to handle the error. A subclass must override this method to provide support for character references outside of the ASCII range.

`handle_entityref` (ref)
  This method is called to process a general entity reference of the form "`&ref;`" where ref is an general entity reference. It looks for ref in the instance (or class) variable `entitydefs` which should be a mapping from entity names to corresponding translations. If a translation is found, it calls the method `handle_data()` with the translation; otherwise, it calls the method `unknown_entityref(ref)`. The default `entitydefs` defines translations for `&amp;`, `&apos`, `&gt;`, `&lt;`, and `&quot;`.

`handle_comment` (comment)
  This method is called when a comment is encountered. The comment argument is a string containing the text between the "`<!-`" and "`->`" delimiters, but not the delimiters themselves. For example, the comment "`<!-text->`" will cause this method to be called with the argument `'text'`. The default method does nothing.

`handle_cdata` (data)
  This method is called when a CDATA element is encountered. The data argument is a string containing the text between the "`<![CDATA[`" and "`]]>`" delimiters, but not the delimiters themselves. For example, the entity "`<![CDATA[text]]>`" will cause this method to be called with the argument `'text'`. The default method does nothing, and is intended to be overridden.

`handle_proc` (name, data)
  This method is called when a processing instruction (PI) is encountered. The name is the PI target, and the data argument is a string containing the text between the PI target and the closing delimiter, but not the delimiter itself. For example, the instruction "`<?XML text?>`" will cause this method to be called with the arguments `'XML'` and `'text'`. The default method does nothing. Note that if a document starts with "`<?xml ..?>`", `handle_xml()` is called to handle it.

`handle_special` (data)
  This method is called when a declaration is encountered. The data argument is a string containing the text between the "`<!`" and "`>`" delimiters, but not the delimiters themselves. For example, the entity "`<!ENTITY text>`" will cause this method to be called with the argument `'ENTITY text'`. The default method does nothing. Note that "`<!DOCTYPE ...>`" is handled separately if it is located at the start of the document.

`syntax_error` (message)
  This method is called when a syntax error is encountered. The message is a description of what was wrong. The default method raises a `RuntimeError` exception. If this method is overridden, it is permissable for it to return. This method is only called when the error can be recovered from. Unrecoverable errors raise a `RuntimeError` without first calling `syntax_error()`.

`unknown_starttag` (tag, attributes)
  This method is called to process an unknown start tag. It is intended to be overridden by a derived class; the base class implementation does nothing.

`unknown_endtag` (tag)
  This method is called to process an unknown end tag. It is intended to be overridden by a derived class; the base class implementation does nothing.

`unknown_charref` (ref)
  This method is called to process unresolvable numeric character references. It is intended to be overridden by a derived class; the base class implementation does nothing.

`unknown_entityref` (ref)
  This method is called to process an unknown entity reference. It is intended to be overridden by a derived class; the base class implementation does nothing.

- 12.3.1 XML Namespaces