19.1. "HTMLParser" — Simple HTML and XHTML parser
*************************************************
Note: The "HTMLParser" module has been renamed to "html.parser" in
Python 3. The *2to3* tool will automatically adapt imports when
converting your sources to Python 3.
New in version 2.2.
**Source code:** Lib/HTMLParser.py
======================================================================
This module defines a class "HTMLParser" which serves as the basis for
parsing text files formatted in HTML (HyperText Mark-up Language) and
XHTML. Unlike the parser in "htmllib", this parser is not based on the
SGML parser in "sgmllib".
class HTMLParser.HTMLParser
An "HTMLParser" instance is fed HTML data and calls handler methods
when start tags, end tags, text, comments, and other markup
elements are encountered. The user should subclass "HTMLParser"
and override its methods to implement the desired behavior.
The "HTMLParser" class is instantiated without arguments.
Unlike the parser in "htmllib", this parser does not check that end
tags match start tags or call the end-tag handler for elements
which are closed implicitly by closing an outer element.
An exception is defined as well:
exception HTMLParser.HTMLParseError
"HTMLParser" is able to handle broken markup, but in some cases it
might raise this exception when it encounters an error while
parsing. This exception provides three attributes: "msg" is a brief
message explaining the error, "lineno" is the number of the line on
which the broken construct was detected, and "offset" is the number
of characters into the line at which the construct starts.
19.1.1. Example HTML Parser Application
=======================================
As a basic example, below is a simple HTML parser that uses the
"HTMLParser" class to print out start tags, end tags and data as they
are encountered:
from HTMLParser import HTMLParser
# create a subclass and override the handler methods
class MyHTMLParser(HTMLParser):
def handle_starttag(self, tag, attrs):
print "Encountered a start tag:", tag
def handle_endtag(self, tag):
print "Encountered an end tag :", tag
def handle_data(self, data):
print "Encountered some data :", data
# instantiate the parser and fed it some HTML
parser = MyHTMLParser()
parser.feed('
Test'
'Parse me!
')
The output will then be:
Encountered a start tag: html
Encountered a start tag: head
Encountered a start tag: title
Encountered some data : Test
Encountered an end tag : title
Encountered an end tag : head
Encountered a start tag: body
Encountered a start tag: h1
Encountered some data : Parse me!
Encountered an end tag : h1
Encountered an end tag : body
Encountered an end tag : html
19.1.2. "HTMLParser" Methods
============================
"HTMLParser" instances have the following methods:
HTMLParser.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. *data* can be either
"unicode" or "str", but passing "unicode" is advised.
HTMLParser.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 the "HTMLParser" base class
method "close()".
HTMLParser.reset()
Reset the instance. Loses all unprocessed data. This is called
implicitly at instantiation time.
HTMLParser.getpos()
Return current line number and offset.
HTMLParser.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.).
The following methods are called when data or markup elements are
encountered and they are meant to be overridden in a subclass. The
base class implementations do nothing (except for
"handle_startendtag()"):
HTMLParser.handle_starttag(tag, attrs)
This method is called to handle the start of a tag (e.g. "").
The *tag* argument is the name of the tag converted to lower case.
The *attrs* argument is a list of "(name, value)" pairs containing
the attributes found inside the tag’s "<>" brackets. The *name*
will be translated to lower case, and quotes in the *value* have
been removed, and character and entity references have been
replaced.
For instance, for the tag "
", this
method would be called as "handle_starttag('a', [('href',
'https://www.cwi.nl/')])".
Changed in version 2.6: All entity references from "htmlentitydefs"
are now replaced in the attribute values.
HTMLParser.handle_endtag(tag)
This method is called to handle the end tag of an element (e.g.
" ").
The *tag* argument is the name of the tag converted to lower case.
HTMLParser.handle_startendtag(tag, attrs)
Similar to "handle_starttag()", but called when the parser
encounters an XHTML-style empty tag (""). This method
may be overridden by subclasses which require this particular
lexical information; the default implementation simply calls
"handle_starttag()" and "handle_endtag()".
HTMLParser.handle_data(data)
This method is called to process arbitrary data (e.g. text nodes
and the content of "" and
"").
HTMLParser.handle_entityref(name)
This method is called to process a named character reference of the
form "&name;" (e.g. ">"), where *name* is a general entity
reference (e.g. "'gt'").
HTMLParser.handle_charref(name)
This method is called to process decimal and hexadecimal numeric
character references of the form "NNN;" and "NNN;". For
example, the decimal equivalent for ">" is ">", whereas the
hexadecimal is ">"; in this case the method will receive
"'62'" or "'x3E'".
HTMLParser.handle_comment(data)
This method is called when a comment is encountered (e.g. "").
For example, the comment "" will cause this method
to be called with the argument "' comment '".
The content of Internet Explorer conditional comments (condcoms)
will also be sent to this method, so, for "", this method will receive
"'[if IE 9]>IE9-specific content").
The *decl* parameter will be the entire contents of the declaration
inside the "" markup (e.g. "'DOCTYPE html'").
HTMLParser.handle_pi(data)
This method is called when a processing instruction is encountered.
The *data* parameter will contain the entire processing
instruction. For example, for the processing instruction "", this method would be called as "handle_pi("proc
color='red'")".
Note: The "HTMLParser" class uses the SGML syntactic rules for
processing instructions. An XHTML processing instruction using
the trailing "'?'" will cause the "'?'" to be included in *data*.
HTMLParser.unknown_decl(data)
This method is called when an unrecognized declaration is read by
the parser.
The *data* parameter will be the entire contents of the declaration
inside the "" markup. It is sometimes useful to be
overridden by a derived class.
19.1.3. Examples
================
The following class implements a parser that will be used to
illustrate more examples:
from HTMLParser import HTMLParser
from htmlentitydefs import name2codepoint
class MyHTMLParser(HTMLParser):
def handle_starttag(self, tag, attrs):
print "Start tag:", tag
for attr in attrs:
print " attr:", attr
def handle_endtag(self, tag):
print "End tag :", tag
def handle_data(self, data):
print "Data :", data
def handle_comment(self, data):
print "Comment :", data
def handle_entityref(self, name):
c = unichr(name2codepoint[name])
print "Named ent:", c
def handle_charref(self, name):
if name.startswith('x'):
c = unichr(int(name[1:], 16))
else:
c = unichr(int(name))
print "Num ent :", c
def handle_decl(self, data):
print "Decl :", data
parser = MyHTMLParser()
Parsing a doctype:
>>> parser.feed('')
Decl : DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"
Parsing an element with a few attributes and a title:
>>> parser.feed('')
Start tag: img
attr: ('src', 'python-logo.png')
attr: ('alt', 'The Python logo')
>>>
>>> parser.feed('Python
')
Start tag: h1
Data : Python
End tag : h1
The content of "script" and "style" elements is returned as is,
without further parsing:
>>> parser.feed('')
Start tag: style
attr: ('type', 'text/css')
Data : #python { color: green }
End tag : style
>>> parser.feed('')
Start tag: script
attr: ('type', 'text/javascript')
Data : alert("hello!");
End tag : script
Parsing comments:
>>> parser.feed(''
... '')
Comment : a comment
Comment : [if IE 9]>IE-specific content'"):
>>> parser.feed('>>>')
Named ent: >
Num ent : >
Num ent : >
Feeding incomplete chunks to "feed()" works, but "handle_data()" might
be called more than once:
>>> for chunk in ['buff', 'ered ', 'text']:
... parser.feed(chunk)
...
Start tag: span
Data : buff
Data : ered
Data : text
End tag : span
Parsing invalid HTML (e.g. unquoted attributes) also works:
>>> parser.feed('tag soup
')
Start tag: p
Start tag: a
attr: ('class', 'link')
attr: ('href', '#main')
Data : tag soup
End tag : p
End tag : a