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{htmlentitydefs}{Definition of replacement text for HTML
  74                              2.0 entities.}
  75   \seemodule{sgmllib}{Base class for \class{HTMLParser}.}
  76 \end{seealso}
  77
  78
  79 \subsection{HTMLParser Objects \label{html-parser-objects}}
  80
  81 In addition to tag methods, the \class{HTMLParser} class provides some
  82 additional methods and instance variables for use within tag methods.
  83
  84 \begin{memberdesc}{formatter}
  85 This is the formatter instance associated with the parser.
  86 \end{memberdesc}
  87
  88 \begin{memberdesc}{nofill}
  89 Boolean flag which should be true when whitespace should not be
  90 collapsed, or false when it should be.  In general, this should only
  91 be true when character data is to be treated as ``preformatted'' text,
  92 as within a \code{<PRE>} element.  The default value is false.  This
  93 affects the operation of \method{handle_data()} and \method{save_end()}.
  94 \end{memberdesc}
  95
  96
  97 \begin{methoddesc}{anchor_bgn}{href, name, type}
  98 This method is called at the start of an anchor region.  The arguments
  99 correspond to the attributes of the \code{<A>} tag with the same
 100 names.  The default implementation maintains a list of hyperlinks
 101 (defined by the \code{HREF} attribute for \code{<A>} tags) within the
 102 document.  The list of hyperlinks is available as the data attribute
 103 \member{anchorlist}.
 104 \end{methoddesc}
 105
 106 \begin{methoddesc}{anchor_end}{}
 107 This method is called at the end of an anchor region.  The default
 108 implementation adds a textual footnote marker using an index into the
 109 list of hyperlinks created by \method{anchor_bgn()}.
 110 \end{methoddesc}
 111
 112 \begin{methoddesc}{handle_image}{source, alt\optional{, ismap\optional{, align\optional{, width\optional{, height}}}}}
 113 This method is called to handle images.  The default implementation
 114 simply passes the \var{alt} value to the \method{handle_data()}
 115 method.
 116 \end{methoddesc}
 117
 118 \begin{methoddesc}{save_bgn}{}
 119 Begins saving character data in a buffer instead of sending it to the
 120 formatter object.  Retrieve the stored data via \method{save_end()}.
 121 Use of the \method{save_bgn()} / \method{save_end()} pair may not be
 122 nested.
 123 \end{methoddesc}
 124
 125 \begin{methoddesc}{save_end}{}
 126 Ends buffering character data and returns all data saved since the
 127 preceding call to \method{save_bgn()}.  If the \member{nofill} flag is
 128 false, whitespace is collapsed to single spaces.  A call to this
 129 method without a preceding call to \method{save_bgn()} will raise a
 130 \exception{TypeError} exception.
 131 \end{methoddesc}
 132
 133
 134
 135 \section{\module{htmlentitydefs} ---
 136          Definitions of HTML general entities}
 137
 138 \declaremodule{standard}{htmlentitydefs}
 139 \modulesynopsis{Definitions of HTML general entities.}
 140 \sectionauthor{Fred L. Drake, Jr.}{fdrake@acm.org}
 141
 142 This module defines a single dictionary, \code{entitydefs}, which is
 143 used by the \refmodule{htmllib} module to provide the
 144 \member{entitydefs} member of the \class{HTMLParser} class.  The
 145 definition provided here contains all the entities defined by HTML 2.0
 146 that can be handled using simple textual substitution in the Latin-1
 147 character set (ISO-8859-1).
 148
 149
 150 \begin{datadesc}{entitydefs}
 151   A dictionary mapping HTML 2.0 entity definitions to their
 152   replacement text in ISO Latin-1.
 153 \end{datadesc}