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.
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The SGMLParser class is instantiated without arguments.
The parser is hardcoded to recognize the following
constructs:
- Opening and closing tags of the form
"<tag attr="value" ...>" and
"</tag>", respectively.
- Numeric character references of the form "&#name;".
- Entity references of the form "&name;".
- SGML comments of the form "<!-text->". Note that
spaces, tabs, and newlines are allowed between the trailing
">" and the immediately preceding "-".
SGMLParser instances have the following interface methods:
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Reset the instance. Loses all unprocessed data. This is called
implicitly at instantiation time.
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Stop processing tags. Treat all following input as literal input
(CDATA). (This is only provided so the HTML tag
<PLAINTEXT> can be implemented.)
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Enter literal mode (CDATA mode).
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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.
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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().
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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.).
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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
and double quotes and backslashes in the value have been interpreted.
For instance, for the tag <A HREF="http://www.cwi.nl/">, 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.
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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.
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This method is called to process arbitrary data. It is intended to be
overridden by a derived class; the base class implementation does
nothing.
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This method is called to process a character reference of the form
"&#ref;". In the base implementation, ref must
be a decimal 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 named
character entities.
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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
&, &apos, >, <, and
".
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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.
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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.
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This method is called when an end tag is found which does not
correspond to any open element.
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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.
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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.
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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.
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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:
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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.
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This method is called to process an opening tag tag that does
not come with a matching closing tag. The attributes argument
has the same meaning as described for handle_starttag() above.
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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.
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