cpython: 1850f45f6169 (original) (raw)

--- a/Doc/library/html.parser.rst +++ b/Doc/library/html.parser.rst @@ -19,14 +19,15 @@ parsing text files formatted in HTML (Hy .. class:: HTMLParser(strict=True) Create a parser instance. If strict is True (the default), invalid

html results in :exc:~html.parser.HTMLParseError exceptions [#]_. If

HTML results in :exc:~html.parser.HTMLParseError exceptions [#]_. If strict is False, the parser uses heuristics to make a best guess at

the intention of any invalid html it encounters, similar to the way most
browsers do.

the intention of any invalid HTML it encounters, similar to the way most
browsers do. Using strict=False is advised.

An :class:HTMLParser instance is fed HTML data and calls handler functions when tags
begin and end. The :class:HTMLParser class is meant to be overridden by the
user to provide a desired behavior.

An :class:.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 :class:.HTMLParser and override its
methods to implement the desired behavior. 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. @@ -39,25 +40,61 @@ An exception is defined as well: .. exception:: HTMLParseError Exception raised by the :class:HTMLParser class when it encounters an error

while parsing. This exception provides three attributes: :attr:msg is a brief
message explaining the error, :attr:lineno is the number of the line on which
the broken construct was detected, and :attr:offset is the number of
characters into the line at which the construct starts.

while parsing and strict is True. This exception provides three
attributes: :attr:msg is a brief message explaining the error,
:attr:lineno is the number of the line on which the broken construct was
detected, and :attr:offset is the number of characters into the line at
which the construct starts. +

+ +Example HTML Parser Application +------------------------------- + +As a basic example, below is a simple HTML parser that uses the +:class:HTMLParser class to print out start tags, end tags, and data +as they are encountered:: +

from html.parser import HTMLParser +
class MyHTMLParser(HTMLParser):

  def handle_starttag(self, tag, attrs):[](#l1.50)

      print("Encountered a start tag:", tag)[](#l1.51)

  def handle_endtag(self, tag):[](#l1.52)

      print("Encountered an end tag :", tag)[](#l1.53)

  def handle_data(self, data):[](#l1.54)

      print("Encountered some data  :", data)[](#l1.55)

parser = MyHTMLParser(strict=False)
parser.feed('Test'

          '<body><h1>Parse me!</h1></body></html>')[](#l1.59)

+ +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 +

+ +:class:.HTMLParser Methods +---------------------------- :class:HTMLParser instances have the following methods: -.. method:: HTMLParser.reset() -

Reset the instance. Loses all unprocessed data. This is called implicitly at
instantiation time. -

- .. method:: 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

:meth:close is called.

:meth:close is called. data must be :class:str.

.. method:: HTMLParser.close() @@ -68,6 +105,12 @@ An exception is defined as well: the :class:HTMLParser base class method :meth:close. +.. method:: HTMLParser.reset() +

Reset the instance. Loses all unprocessed data. This is called implicitly at
instantiation time. +

+ .. method:: HTMLParser.getpos() Return current line number and offset. @@ -81,23 +124,35 @@ An exception is defined as well: 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 :meth:~HTMLParser.handle_startendtag): + + .. method:: HTMLParser.handle_starttag(tag, attrs)

This method is called to handle the start of a tag. It is intended to be
overridden by a derived class; the base class implementation does nothing.

This method is called to handle the start of a tag (e.g. <div id="main">). 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 ``<A
HREF="``" title="undefined" rel="noopener noreferrer">http://www.cwi.nl/">``, this method would be called as
handle_starttag('a', [('href', 'http://www.cwi.nl/')]).

have been replaced. +
For instance, for the tag <A HREF="http://www.cwi.nl/">, this method
would be called as handle_starttag('a', [('href', 'http://www.cwi.nl/')]). All entity references from :mod:html.entities are replaced in the attribute values.

+.. method:: HTMLParser.handle_endtag(tag) +

This method is called to handle the end tag of an element (e.g. </div>). +
The tag argument is the name of the tag converted to lower case. +

+ .. method:: HTMLParser.handle_startendtag(tag, attrs) Similar to :meth:handle_starttag, but called when the parser encounters an @@ -106,57 +161,46 @@ An exception is defined as well: implementation simply calls :meth:handle_starttag and :meth:handle_endtag. -.. method:: HTMLParser.handle_endtag(tag) -

This method is called to handle the end tag of an element. It is intended to be
overridden by a derived class; the base class implementation does nothing. The
tag argument is the name of the tag converted to lower case. -

- .. method:: HTMLParser.handle_data(data)

This method is called to process arbitrary data (e.g. the content of
<script>...</script> and <style>...</style>). It is intended to be
overridden by a derived class; the base class implementation does nothing. -

- -.. method:: HTMLParser.handle_charref(name) -

This method is called to process a character reference of the form &#ref;.
It is intended to be overridden by a derived class; the base class
implementation does nothing.

This method is called to process arbitrary data (e.g. text nodes and the
content of <script>...</script> and <style>...</style>).

.. method:: HTMLParser.handle_entityref(name)

This method is called to process a general entity reference of the form
&name; where name is an general entity reference. It is intended to be
overridden by a derived class; the base class implementation does nothing.

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'). +

+ +.. method:: HTMLParser.handle_charref(name) +

This method is called to process decimal and hexadecimal numeric character
references of the form &#NNN; and &#xNNN;. For example, the decimal
equivalent for > is >, whereas the hexadecimal is >;
in this case the method will receive '62' or 'x3E'.

.. method:: HTMLParser.handle_comment(data)

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  will cause
this method to be called with the argument 'text'. It is intended to be
overridden by a derived class; the base class implementation does nothing.

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]>IE-specific content<![endif]'.

.. method:: HTMLParser.handle_decl(decl)

Method called when an SGML doctype declaration is read by the parser.
The decl parameter will be the entire contents of the declaration inside
the <!...> markup. It is intended to be overridden by a derived class;
the base class implementation does nothing. -

This method is called to handle an HTML doctype declaration (e.g.
<!DOCTYPE html>).

-.. method:: HTMLParser.unknown_decl(data) -

Method called when an unrecognized SGML 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; the base class implementation raises an :exc:HTMLParseError.

The decl parameter will be the entire contents of the declaration inside
the <!...> markup (e.g. 'DOCTYPE html').

.. method:: HTMLParser.handle_pi(data) @@ -174,29 +218,123 @@ An exception is defined as well: cause the '?' to be included in data. -.. _htmlparser-example: +.. method:: 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. The base class implementation raises an :exc:HTMLParseError
when strict is True.

-Example HTML Parser Application -------------------------------- + +.. _htmlparser-examples: -As a basic example, below is a simple HTML parser that uses the -:class:HTMLParser class to print out start tags, end tags, and data -as they are encountered:: +Examples +-------- + +The following class implements a parser that will be used to illustrate more +examples:: from html.parser import HTMLParser

from html.entities import name2codepoint class MyHTMLParser(HTMLParser): def handle_starttag(self, tag, attrs):

      print("Encountered a start tag:", tag)[](#l1.268)

      print("Start tag:", tag)[](#l1.269)

```
      for attr in attrs:[](#l1.270)
```

          print("     attr:", attr)[](#l1.271)
  def handle_endtag(self, tag):[](#l1.272)

      print("Encountered  an end tag:", tag)[](#l1.273)

      print("End tag  :", tag)[](#l1.274)
  def handle_data(self, data):[](#l1.275)

      print("Encountered   some data:", data)[](#l1.276)

      print("Data     :", data)[](#l1.277)

  def handle_comment(self, data):[](#l1.278)

      print("Comment  :", data)[](#l1.279)

  def handle_entityref(self, name):[](#l1.280)

      c = chr(name2codepoint[name])[](#l1.281)

```
      print("Named ent:", c)[](#l1.282)
```

  def handle_charref(self, name):[](#l1.283)

      if name.startswith('x'):[](#l1.284)

          c = chr(int(name[1:], 16))[](#l1.285)

```
      else:[](#l1.286)
```
```
          c = chr(int(name))[](#l1.287)
```
```
      print("Num ent  :", c)[](#l1.288)
```

  def handle_decl(self, data):[](#l1.289)

      print("Decl     :", data)[](#l1.290)

parser = MyHTMLParser(strict=False) +

+Parsing a doctype:: +

parser.feed('<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" '
... '"')[](#l1.297)" title="undefined" rel="noopener noreferrer">http://www.w3.org/TR/html4/strict.dtd">')[](#l1.297)
Decl : DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"[](#l1.298) +

+Parsing an element with a few attributes and a title:: +

parser.feed('')
Start tag: img

   attr: ('src', 'python-logo.png')[](#l1.304)

   attr: ('alt', 'The Python logo')[](#l1.305)

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 = MyHTMLParser()
parser.feed('Test'

          '<body><h1>Parse me!</h1></body></html>')[](#l1.317)

parser.feed('')
Start tag: style

   attr: ('type', 'text/css')[](#l1.320)

Data : #python { color: green }
End tag : style
parser.feed('')
Start tag: script

   attr: ('type', 'text/javascript')[](#l1.327)

Data : alert("hello!");
End tag : script +

+Parsing comments:: +

parser.feed(''
... '')
Comment : a comment
Comment : [if IE 9]>IE-specific content<![endif] +

+Parsing named and numeric character references and converting them to the +correct char (note: these 3 references are all equivalent to '>')::

parser.feed('>>>')
Named ent: >
Num ent : >
Num ent : > +

+Feeding incomplete chunks to :meth:~HTMLParser.feed works, but +:meth:~HTMLParser.handle_data might be called more than once:: +

for chunk in ['<sp', 'an>buff', 'ered ', 'text</s', 'pan>']:
... 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')[](#l1.363)
```
```
   attr: ('href', '#main')[](#l1.364)
```
Data : tag soup
End tag : p
End tag : a

.. rubric:: Footnotes