19.2. "sgmllib" — Simple SGML parser
************************************
Deprecated since version 2.6: The "sgmllib" module has been removed in
Python 3.
This module defines a class "SGMLParser" which serves as the basis for
parsing text files formatted in SGML (Standard Generalized Mark-up
Language). In fact, it does not provide a full SGML parser — it only
parses SGML insofar as it is used by HTML, and the module only exists
as a base for the "htmllib" module. Another HTML parser which
supports XHTML and offers a somewhat different interface is available
in the "HTMLParser" module.
class sgmllib.SGMLParser
The "SGMLParser" class is instantiated without arguments. The
parser is hardcoded to recognize the following constructs:
* Opening and closing tags of the form ""
and "", respectively.
* Numeric character references of the form "name;".
* Entity references of the form "&name;".
* SGML comments of the form "". Note that spaces,
tabs, and newlines are allowed between the trailing ">" and the
immediately preceding "--".
A single exception is defined as well:
exception sgmllib.SGMLParseError
Exception raised by the "SGMLParser" class when it encounters an
error while parsing.
New in version 2.1.
"SGMLParser" instances have the following methods:
SGMLParser.reset()
Reset the instance. Loses all unprocessed data. This is called
implicitly at instantiation time.
SGMLParser.setnomoretags()
Stop processing tags. Treat all following input as literal input
(CDATA). (This is only provided so the HTML tag "" can
be implemented.)
SGMLParser.setliteral()
Enter literal mode (CDATA mode).
SGMLParser.feed(data)
Feed some text to the parser. It is processed insofar as it
consists of complete elements; incomplete data is buffered until
more data is fed or "close()" is called.
SGMLParser.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()".
SGMLParser.get_starttag_text()
Return the text of the most recently opened start tag. This should
not normally be needed for structured processing, but may be useful
in dealing with HTML “as deployed” or for re-generating input with
minimal changes (whitespace between attributes can be preserved,
etc.).
SGMLParser.handle_starttag(tag, method, attributes)
This method is called to handle start tags for which either a
"start_tag()" or "do_tag()" method has been defined. The *tag*
argument is the name of the tag converted to lower case, and the
*method* argument is the bound method which should be used to
support semantic interpretation of the start tag. The *attributes*
argument is a list of "(name, value)" pairs containing the
attributes found inside the tag’s "<>" brackets.
The *name* has been translated to lower case. Double quotes and
backslashes in the *value* have been interpreted, as well as known
character references and known entity references terminated by a
semicolon (normally, entity references can be terminated by any
non-alphanumerical character, but this would break the very common
case of "" when "eggs" is a valid
entity name).
For instance, for the tag "", this
method would be called as "unknown_starttag('a', [('href',
'http://www.cwi.nl/')])". The base implementation simply calls
*method* with *attributes* as the only argument.
New in version 2.5: Handling of entity and character references
within attribute values.
SGMLParser.handle_endtag(tag, method)
This method is called to handle endtags for which an "end_tag()"
method has been defined. The *tag* argument is the name of the tag
converted to lower case, and the *method* argument is the bound
method which should be used to support semantic interpretation of
the end tag. If no "end_tag()" method is defined for the closing
element, this handler is not called. The base implementation
simply calls *method*.
SGMLParser.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.
SGMLParser.handle_charref(ref)
This method is called to process a character reference of the form
"ref;". The base implementation uses "convert_charref()" to
convert the reference to a string. If that method returns a
string, it is passed to "handle_data()", otherwise
"unknown_charref(ref)" is called to handle the error.
Changed in version 2.5: Use "convert_charref()" instead of hard-
coding the conversion.
SGMLParser.convert_charref(ref)
Convert a character reference to a string, or "None". *ref* is the
reference passed in as a string. In the base implementation, *ref*
must be a decimal number in the range 0–255. It converts the code
point found using the "convert_codepoint()" method. If *ref* is
invalid or out of range, this method returns "None". This method
is called by the default "handle_charref()" implementation and by
the attribute value parser.
New in version 2.5.
SGMLParser.convert_codepoint(codepoint)
Convert a code point to a "str" value. Encodings can be handled
here if appropriate, though the rest of "sgmllib" is oblivious on
this matter.
New in version 2.5.
SGMLParser.handle_entityref(ref)
This method is called to process a general entity reference of the
form "&ref;" where *ref* is a general entity reference. It
converts *ref* by passing it to "convert_entityref()". If a
translation is returned, it calls the method "handle_data()" with
the translation; otherwise, it calls the method
"unknown_entityref(ref)". The default "entitydefs" defines
translations for "&", "'", ">", "<", and """.
Changed in version 2.5: Use "convert_entityref()" instead of hard-
coding the conversion.
SGMLParser.convert_entityref(ref)
Convert a named entity reference to a "str" value, or "None". The
resulting value will not be parsed. *ref* will be only the name of
the entity. The default implementation looks for *ref* in the
instance (or class) variable "entitydefs" which should be a mapping
from entity names to corresponding translations. If no translation
is available for *ref*, this method returns "None". This method is
called by the default "handle_entityref()" implementation and by
the attribute value parser.
New in version 2.5.
SGMLParser.handle_comment(comment)
This method is called when a comment is encountered. The *comment*
argument is a string containing the text between the "" delimiters, but not the delimiters themselves. For example,
the comment "" will cause this method to be called with
the argument "'text'". The default method does nothing.
SGMLParser.handle_decl(data)
Method called when an SGML declaration is read by the parser. In
practice, the "DOCTYPE" declaration is the only thing observed in
HTML, but the parser does not discriminate among different (or
broken) declarations. Internal subsets in a "DOCTYPE" declaration
are not supported. The *data* parameter will be the entire
contents of the declaration inside the "" markup. The
default implementation does nothing.
SGMLParser.report_unbalanced(tag)
This method is called when an end tag is found which does not
correspond to any open element.
SGMLParser.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.
SGMLParser.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.
SGMLParser.unknown_charref(ref)
This method is called to process unresolvable numeric character
references. Refer to "handle_charref()" to determine what is
handled by default. It is intended to be overridden by a derived
class; the base class implementation does nothing.
SGMLParser.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.
Apart from overriding or extending the methods listed above, derived
classes may also define methods of the following form to define
processing of specific tags. Tag names in the input stream are case
independent; the *tag* occurring in method names must be in lower
case:
SGMLParser.start_tag(attributes)
This method is called to process an opening tag *tag*. It has
preference over "do_tag()". The *attributes* argument has the same
meaning as described for "handle_starttag()" above.
SGMLParser.do_tag(attributes)
This method is called to process an opening tag *tag* for which no
"start_tag()" method is defined. The *attributes* argument has
the same meaning as described for "handle_starttag()" above.
SGMLParser.end_tag()
This method is called to process a closing tag *tag*.
Note that the parser maintains a stack of open elements for which no
end tag has been found yet. Only tags processed by "start_tag()" are
pushed on this stack. Definition of an "end_tag()" method is optional
for these tags. For tags processed by "do_tag()" or by
"unknown_tag()", no "end_tag()" method must be defined; if defined, it
will not be used. If both "start_tag()" and "do_tag()" methods exist
for a tag, the "start_tag()" method takes precedence.