Doc/lib/libhtmllib.tex

   1 \section{\module{htmllib} ---
   2          A parser for HTML documents}
   3
   4 \declaremodule{standard}{htmllib}
   5 \modulesynopsis{A parser for HTML documents.}
   6
   7 \index{HTML}
   8 \index{hypertext}
   9
  10
  11 This module defines a class which can serve as a base for parsing text
  12 files formatted in the HyperText Mark-up Language (HTML).  The class
  13 is not directly concerned with I/O --- it must be provided with input
  14 in string form via a method, and makes calls to methods of a
  15 ``formatter'' object in order to produce output.  The
  16 \class{HTMLParser} class is designed to be used as a base class for
  17 other classes in order to add functionality, and allows most of its
  18 methods to be extended or overridden.  In turn, this class is derived
  19 from and extends the \class{SGMLParser} class defined in module
  20 \refmodule{sgmllib}\refstmodindex{sgmllib}.  The \class{HTMLParser}
  21 implementation supports the HTML 2.0 language as described in
  22 \rfc{1866}.  Two implementations of formatter objects are provided in
  23 the \refmodule{formatter}\refstmodindex{formatter}\ module; refer to the
  24 documentation for that module for information on the formatter
  25 interface.
  26 \withsubitem{(in module sgmllib)}{\ttindex{SGMLParser}}
  27
  28 The following is a summary of the interface defined by
  29 \class{sgmllib.SGMLParser}:
  30
  31 \begin{itemize}
  32
  33 \item
  34 The interface to feed data to an instance is through the \method{feed()}
  35 method, which takes a string argument.  This can be called with as
  36 little or as much text at a time as desired; \samp{p.feed(a);
  37 p.feed(b)} has the same effect as \samp{p.feed(a+b)}.  When the data
  38 contains complete HTML tags, these are processed immediately;
  39 incomplete elements are saved in a buffer.  To force processing of all
  40 unprocessed data, call the \method{close()} method.
  41
  42 For example, to parse the entire contents of a file, use:
  43 \begin{verbatim}
  44 parser.feed(open('myfile.html').read())
  45 parser.close()
  46 \end{verbatim}
  47
  48 \item
  49 The interface to define semantics for HTML tags is very simple: derive
  50 a class and define methods called \method{start_\var{tag}()},
  51 \method{end_\var{tag}()}, or \method{do_\var{tag}()}.  The parser will
  52 call these at appropriate moments: \method{start_\var{tag}} or
  53 \method{do_\var{tag}()} is called when an opening tag of the form
  54 \code{<\var{tag} ...>} is encountered; \method{end_\var{tag}()} is called
  55 when a closing tag of the form \code{<\var{tag}>} is encountered.  If
  56 an opening tag requires a corresponding closing tag, like \code{<H1>}
  57 ... \code{</H1>}, the class should define the \method{start_\var{tag}()}
  58 method; if a tag requires no closing tag, like \code{<P>}, the class
  59 should define the \method{do_\var{tag}()} method.
  60
  61 \end{itemize}
  62
  63 The module defines a single class:
  64
  65 \begin{classdesc}{HTMLParser}{formatter}
  66 This is the basic HTML parser class.  It supports all entity names
  67 required by the HTML 2.0 specification (\rfc{1866}).  It also defines
  68 handlers for all HTML 2.0 and many HTML 3.0 and 3.2 elements.
  69 \end{classdesc}
  70
  71
  72 \begin{seealso}
  73   \seemodule{formatter}{Interface definition for transforming an
  74                         abstract flow of formatting events into
  75                         specific output events on writer objects.}
  76   \seemodule{HTMLParser}{Alternate HTML parser that offers a slightly
  77                          lower-level view of the input, but is
  78                          designed to work with XHTML, and does not
  79                          implement some of the SGML syntax not used in
  80                          ``HTML as deployed'' and which isn't legal
  81                          for XHTML.}
  82   \seemodule{htmlentitydefs}{Definition of replacement text for HTML
  83                              2.0 entities.}
  84   \seemodule{sgmllib}{Base class for \class{HTMLParser}.}
  85 \end{seealso}
  86
  87
  88 \subsection{HTMLParser Objects \label{html-parser-objects}}
  89
  90 In addition to tag methods, the \class{HTMLParser} class provides some
  91 additional methods and instance variables for use within tag methods.
  92
  93 \begin{memberdesc}{formatter}
  94 This is the formatter instance associated with the parser.
  95 \end{memberdesc}
  96
  97 \begin{memberdesc}{nofill}
  98 Boolean flag which should be true when whitespace should not be
  99 collapsed, or false when it should be.  In general, this should only
 100 be true when character data is to be treated as ``preformatted'' text,
 101 as within a \code{<PRE>} element.  The default value is false.  This
 102 affects the operation of \method{handle_data()} and \method{save_end()}.
 103 \end{memberdesc}
 104
 105
 106 \begin{methoddesc}{anchor_bgn}{href, name, type}
 107 This method is called at the start of an anchor region.  The arguments
 108 correspond to the attributes of the \code{<A>} tag with the same
 109 names.  The default implementation maintains a list of hyperlinks
 110 (defined by the \code{HREF} attribute for \code{<A>} tags) within the
 111 document.  The list of hyperlinks is available as the data attribute
 112 \member{anchorlist}.
 113 \end{methoddesc}
 114
 115 \begin{methoddesc}{anchor_end}{}
 116 This method is called at the end of an anchor region.  The default
 117 implementation adds a textual footnote marker using an index into the
 118 list of hyperlinks created by \method{anchor_bgn()}.
 119 \end{methoddesc}
 120
 121 \begin{methoddesc}{handle_image}{source, alt\optional{, ismap\optional{, align\optional{, width\optional{, height}}}}}
 122 This method is called to handle images.  The default implementation
 123 simply passes the \var{alt} value to the \method{handle_data()}
 124 method.
 125 \end{methoddesc}
 126
 127 \begin{methoddesc}{save_bgn}{}
 128 Begins saving character data in a buffer instead of sending it to the
 129 formatter object.  Retrieve the stored data via \method{save_end()}.
 130 Use of the \method{save_bgn()} / \method{save_end()} pair may not be
 131 nested.
 132 \end{methoddesc}
 133
 134 \begin{methoddesc}{save_end}{}
 135 Ends buffering character data and returns all data saved since the
 136 preceding call to \method{save_bgn()}.  If the \member{nofill} flag is
 137 false, whitespace is collapsed to single spaces.  A call to this
 138 method without a preceding call to \method{save_bgn()} will raise a
 139 \exception{TypeError} exception.
 140 \end{methoddesc}
 141
 142
 143
 144 \section{\module{htmlentitydefs} ---
 145          Definitions of HTML general entities}
 146
 147 \declaremodule{standard}{htmlentitydefs}
 148 \modulesynopsis{Definitions of HTML general entities.}
 149 \sectionauthor{Fred L. Drake, Jr.}{fdrake@acm.org}
 150
 151 This module defines three dictionaries, \code{name2codepoint},
 152 \code{codepoint2name}, and \code{entitydefs}. \code{entitydefs} is
 153 used by the \refmodule{htmllib} module to provide the
 154 \member{entitydefs} member of the \class{HTMLParser} class.  The
 155 definition provided here contains all the entities defined by XHTML 1.0
 156 that can be handled using simple textual substitution in the Latin-1
 157 character set (ISO-8859-1).
 158
 159
 160 \begin{datadesc}{entitydefs}
 161   A dictionary mapping XHTML 1.0 entity definitions to their
 162   replacement text in ISO Latin-1.
 163
 164 \end{datadesc}
 165
 166 \begin{datadesc}{name2codepoint}
 167   A dictionary that maps HTML entity names to the Unicode codepoints.
 168   \versionadded{2.3}
 169 \end{datadesc}
 170
 171 \begin{datadesc}{codepoint2name}
 172   A dictionary that maps Unicode codepoints to HTML entity names.
 173   \versionadded{2.3}
 174 \end{datadesc}