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.
classSGMLParser(
)
The SGMLParser class is instantiated without arguments.
The parser is hardcoded to recognize the following
constructs:
Opening and closing tags of the form
"<tagattr="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 "--".
A single exception is defined as well:
exceptionSGMLParseError
Exception raised by the SGMLParser class when it encounters an
error while parsing.
New in version 2.1.
SGMLParser instances have the following methods:
reset(
)
Reset the instance. Loses all unprocessed data. This is called
implicitly at instantiation time.
setnomoretags(
)
Stop processing tags. Treat all following input as literal input
(CDATA). (This is only provided so the HTML tag
<PLAINTEXT> can be implemented.)
setliteral(
)
Enter literal mode (CDATA mode).
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.
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().
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.).
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 <A HREF="url?spam=1&eggs=2"> when eggs
is a valid entity name).
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.
New in version 2.5:
Handling of entity and character references within
attribute values.
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.
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;". 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.
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.
convert_codepoint(
codepoint)
Convert a codepoint 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.
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 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
&, &apos, >, <, and
".
Changed in version 2.5:
Use convert_entityref() instead of hard-coding
the conversion.
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.
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_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.
report_unbalanced(
tag)
This method is called when an end tag is found which does not
correspond to any open element.
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. 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.
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:
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.
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.
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.
