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annotate Doc/lib/libhtmlparser.tex @ 39940:dfd809dcf680 2.5

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Bug #1446043: correctly raise a LookupError if an encoding name given to encodings.search_function() contains a dot. (backport from rev. 52075)
author Georg Brandl <georg@python.org>
date Sat, 30 Sep 2006 11:22:35 +0000
parents 6e0b053c6cf7
children 963c0e442832
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 \section{\module{HTMLParser} ---
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2 Simple HTML and XHTML parser}
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3
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4 \declaremodule{standard}{HTMLParser}
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5 \modulesynopsis{A simple parser that can handle HTML and XHTML.}
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6
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7 \versionadded{2.2}
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8
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9 This module defines a class \class{HTMLParser} which serves as the
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10 basis for parsing text files formatted in HTML\index{HTML} (HyperText
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11 Mark-up Language) and XHTML.\index{XHTML} Unlike the parser in
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12 \refmodule{htmllib}, this parser is not based on the SGML parser in
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13 \refmodule{sgmllib}.
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14
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15
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16 \begin{classdesc}{HTMLParser}{}
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17 The \class{HTMLParser} class is instantiated without arguments.
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18
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19 An HTMLParser instance is fed HTML data and calls handler functions
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20 when tags begin and end. The \class{HTMLParser} class is meant to be
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21 overridden by the user to provide a desired behavior.
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22
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23 Unlike the parser in \refmodule{htmllib}, this parser does not check
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24 that end tags match start tags or call the end-tag handler for
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25 elements which are closed implicitly by closing an outer element.
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26 \end{classdesc}
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27
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28 An exception is defined as well:
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29
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30 \begin{excdesc}{HTMLParseError}
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31 Exception raised by the \class{HTMLParser} class when it encounters an
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32 error while parsing. This exception provides three attributes:
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33 \member{msg} is a brief message explaining the error, \member{lineno}
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34 is the number of the line on which the broken construct was detected,
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35 and \member{offset} is the number of characters into the line at which
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36 the construct starts.
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37 \end{excdesc}
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38
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39
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40 \class{HTMLParser} instances have the following methods:
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41
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42 \begin{methoddesc}{reset}{}
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43 Reset the instance. Loses all unprocessed data. This is called
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44 implicitly at instantiation time.
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45 \end{methoddesc}
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46
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47 \begin{methoddesc}{feed}{data}
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48 Feed some text to the parser. It is processed insofar as it consists
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49 of complete elements; incomplete data is buffered until more data is
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50 fed or \method{close()} is called.
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51 \end{methoddesc}
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52
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53 \begin{methoddesc}{close}{}
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54 Force processing of all buffered data as if it were followed by an
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55 end-of-file mark. This method may be redefined by a derived class to
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56 define additional processing at the end of the input, but the
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57 redefined version should always call the \class{HTMLParser} base class
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58 method \method{close()}.
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59 \end{methoddesc}
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60
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61 \begin{methoddesc}{getpos}{}
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62 Return current line number and offset.
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63 \end{methoddesc}
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64
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65 \begin{methoddesc}{get_starttag_text}{}
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66 Return the text of the most recently opened start tag. This should
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67 not normally be needed for structured processing, but may be useful in
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68 dealing with HTML ``as deployed'' or for re-generating input with
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69 minimal changes (whitespace between attributes can be preserved,
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70 etc.).
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71 \end{methoddesc}
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72
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73 \begin{methoddesc}{handle_starttag}{tag, attrs}
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74 This method is called to handle the start of a tag. It is intended to
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75 be overridden by a derived class; the base class implementation does
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76 nothing.
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77
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78 The \var{tag} argument is the name of the tag converted to
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79 lower case. The \var{attrs} argument is a list of \code{(\var{name},
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80 \var{value})} pairs containing the attributes found inside the tag's
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81 \code{<>} brackets. The \var{name} will be translated to lower case
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82 and double quotes and backslashes in the \var{value} have been
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83 interpreted. For instance, for the tag \code{<A
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84 HREF="http://www.cwi.nl/">}, this method would be called as
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85 \samp{handle_starttag('a', [('href', 'http://www.cwi.nl/')])}.
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86 \end{methoddesc}
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87
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88 \begin{methoddesc}{handle_startendtag}{tag, attrs}
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89 Similar to \method{handle_starttag()}, but called when the parser
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90 encounters an XHTML-style empty tag (\code{<a .../>}). This method
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91 may be overridden by subclasses which require this particular lexical
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92 information; the default implementation simple calls
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93 \method{handle_starttag()} and \method{handle_endtag()}.
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94 \end{methoddesc}
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95
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96 \begin{methoddesc}{handle_endtag}{tag}
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97 This method is called to handle the end tag of an element. It is
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98 intended to be overridden by a derived class; the base class
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99 implementation does nothing. The \var{tag} argument is the name of
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100 the tag converted to lower case.
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101 \end{methoddesc}
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102
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103 \begin{methoddesc}{handle_data}{data}
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104 This method is called to process arbitrary data. It is intended to be
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105 overridden by a derived class; the base class implementation does
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106 nothing.
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107 \end{methoddesc}
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108
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109 \begin{methoddesc}{handle_charref}{name} This method is called to
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110 process a character reference of the form \samp{\&\#\var{ref};}. It
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111 is intended to be overridden by a derived class; the base class
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112 implementation does nothing.
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113 \end{methoddesc}
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114
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115 \begin{methoddesc}{handle_entityref}{name}
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116 This method is called to process a general entity reference of the
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117 form \samp{\&\var{name};} where \var{name} is an general entity
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118 reference. It is intended to be overridden by a derived class; the
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119 base class implementation does nothing.
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120 \end{methoddesc}
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121
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122 \begin{methoddesc}{handle_comment}{data}
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123 This method is called when a comment is encountered. The
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124 \var{comment} argument is a string containing the text between the
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125 \samp{--} and \samp{--} delimiters, but not the delimiters
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126 themselves. For example, the comment \samp{<!--text-->} will
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127 cause this method to be called with the argument \code{'text'}. It is
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128 intended to be overridden by a derived class; the base class
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129 implementation does nothing.
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130 \end{methoddesc}
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131
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132 \begin{methoddesc}{handle_decl}{decl}
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133 Method called when an SGML declaration is read by the parser. The
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134 \var{decl} parameter will be the entire contents of the declaration
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135 inside the \code{<!}...\code{>} markup. It is intended to be overridden
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136 by a derived class; the base class implementation does nothing.
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137 \end{methoddesc}
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138
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139 \begin{methoddesc}{handle_pi}{data}
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140 Method called when a processing instruction is encountered. The
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141 \var{data} parameter will contain the entire processing instruction.
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142 For example, for the processing instruction \code{<?proc color='red'>},
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143 this method would be called as \code{handle_pi("proc color='red'")}. It
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144 is intended to be overridden by a derived class; the base class
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145 implementation does nothing.
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146
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147 \note{The \class{HTMLParser} class uses the SGML syntactic rules for
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148 processing instructions. An XHTML processing instruction using the
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149 trailing \character{?} will cause the \character{?} to be included in
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150 \var{data}.}
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151 \end{methoddesc}
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152
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153
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154 \subsection{Example HTML Parser Application \label{htmlparser-example}}
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155
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156 As a basic example, below is a very basic HTML parser that uses the
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157 \class{HTMLParser} class to print out tags as they are encountered:
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158
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159 \begin{verbatim}
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160 from HTMLParser import HTMLParser
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161
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162 class MyHTMLParser(HTMLParser):
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163
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164 def handle_starttag(self, tag, attrs):
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165 print "Encountered the beginning of a %s tag" % tag
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166
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167 def handle_endtag(self, tag):
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168 print "Encountered the end of a %s tag" % tag
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169 \end{verbatim}