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packages from SVN sources</a></li></ul></li></ul><ul class="menu foreign" id="lxml source howto-menu"><li class="menu title"><a href="lxml-source-howto.html">How to read the source of lxml</a><ul class="submenu"><li class="menu item"><a href="lxml-source-howto.html#what-is-cython">What is Cython?</a></li><li class="menu item"><a href="lxml-source-howto.html#where-to-start">Where to start?</a></li><li class="menu item"><a href="lxml-source-howto.html#lxml-etree">lxml.etree</a></li><li class="menu item"><a href="lxml-source-howto.html#python-modules">Python modules</a></li><li class="menu item"><a href="lxml-source-howto.html#lxml-objectify">lxml.objectify</a></li><li class="menu item"><a href="lxml-source-howto.html#lxml-html">lxml.html</a></li></ul></li></ul><ul class="menu foreign" id="changes 2 3 5-menu"><li class="menu title"><a href="changes-2.3.5.html">Release Changelog</a></li></ul><ul class="menu foreign" id="credits-menu"><li class="menu title"><a href="credits.html">Credits</a><ul class="submenu"><li class="menu item"><a href="credits.html#main-contributors">Main contributors</a></li><li class="menu item"><a href="credits.html#special-thanks-goes-to">Special thanks goes to:</a></li></ul></li></ul></li><li><a href="http://lxml.de/sitemap.html">Sitemap</a></li></ul></div><h1 class="title">Parsing XML and HTML with lxml</h1>
13 <p>lxml provides a very simple and powerful API for parsing XML and HTML. It
14 supports one-step parsing as well as step-by-step parsing using an
15 event-driven API (currently only for XML).</p>
16 <div class="contents topic" id="contents">
17 <p class="topic-title first">Contents</p>
19 <li><a class="reference internal" href="#parsers" id="id1">Parsers</a><ul>
20 <li><a class="reference internal" href="#parser-options" id="id2">Parser options</a></li>
21 <li><a class="reference internal" href="#error-log" id="id3">Error log</a></li>
22 <li><a class="reference internal" href="#parsing-html" id="id4">Parsing HTML</a></li>
23 <li><a class="reference internal" href="#doctype-information" id="id5">Doctype information</a></li>
26 <li><a class="reference internal" href="#the-target-parser-interface" id="id6">The target parser interface</a></li>
27 <li><a class="reference internal" href="#the-feed-parser-interface" id="id7">The feed parser interface</a></li>
28 <li><a class="reference internal" href="#iterparse-and-iterwalk" id="id8">iterparse and iterwalk</a><ul>
29 <li><a class="reference internal" href="#selective-tag-events" id="id9">Selective tag events</a></li>
30 <li><a class="reference internal" href="#comments-and-pis" id="id10">Comments and PIs</a></li>
31 <li><a class="reference internal" href="#modifying-the-tree" id="id11">Modifying the tree</a></li>
32 <li><a class="reference internal" href="#iterwalk" id="id12">iterwalk</a></li>
35 <li><a class="reference internal" href="#python-unicode-strings" id="id13">Python unicode strings</a><ul>
36 <li><a class="reference internal" href="#serialising-to-unicode-strings" id="id14">Serialising to Unicode strings</a></li>
41 <p>The usual setup procedure:</p>
42 <div class="syntax"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">lxml</span> <span class="kn">import</span> <span class="n">etree</span>
44 <div class="section" id="parsers">
46 <p>Parsers are represented by parser objects. There is support for parsing both
47 XML and (broken) HTML. Note that XHTML is best parsed as XML, parsing it with
48 the HTML parser can lead to unexpected results. Here is a simple example for
49 parsing XML from an in-memory string:</p>
50 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">xml</span> <span class="o">=</span> <span class="s">'<a xmlns="test"><b xmlns="test"/></a>'</span>
52 <span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">fromstring</span><span class="p">(</span><span class="n">xml</span><span class="p">)</span>
53 <span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
54 <span class="go">b'<a xmlns="test"><b xmlns="test"/></a>'</span>
56 <p>To read from a file or file-like object, you can use the <tt class="docutils literal">parse()</tt> function,
57 which returns an <tt class="docutils literal">ElementTree</tt> object:</p>
58 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">tree</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">))</span>
59 <span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">getroot</span><span class="p">())</span>
60 <span class="go">b'<a xmlns="test"><b xmlns="test"/></a>'</span>
62 <p>Note how the <tt class="docutils literal">parse()</tt> function reads from a file-like object here. If
63 parsing is done from a real file, it is more common (and also somewhat more
64 efficient) to pass a filename:</p>
65 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">tree</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="s">"doc/test.xml"</span><span class="p">)</span>
67 <p>lxml can parse from a local file, an HTTP URL or an FTP URL. It also
68 auto-detects and reads gzip-compressed XML files (.gz).</p>
69 <p>If you want to parse from memory and still provide a base URL for the document
70 (e.g. to support relative paths in an XInclude), you can pass the <tt class="docutils literal">base_url</tt>
72 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">fromstring</span><span class="p">(</span><span class="n">xml</span><span class="p">,</span> <span class="n">base_url</span><span class="o">=</span><span class="s">"http://where.it/is/from.xml"</span><span class="p">)</span>
74 <div class="section" id="parser-options">
75 <h2>Parser options</h2>
76 <p>The parsers accept a number of setup options as keyword arguments. The above
77 example is easily extended to clean up namespaces during parsing:</p>
78 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLParser</span><span class="p">(</span><span class="n">ns_clean</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
79 <span class="gp">>>> </span><span class="n">tree</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">),</span> <span class="n">parser</span><span class="p">)</span>
80 <span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">getroot</span><span class="p">())</span>
81 <span class="go">b'<a xmlns="test"><b/></a>'</span>
83 <p>The keyword arguments in the constructor are mainly based on the libxml2
84 parser configuration. A DTD will also be loaded if validation or attribute
85 default values are requested.</p>
86 <p>Available boolean keyword arguments:</p>
88 <li>attribute_defaults - read the DTD (if referenced by the document) and add
89 the default attributes from it</li>
90 <li>dtd_validation - validate while parsing (if a DTD was referenced)</li>
91 <li>load_dtd - load and parse the DTD while parsing (no validation is performed)</li>
92 <li>no_network - prevent network access when looking up external
93 documents (on by default)</li>
94 <li>ns_clean - try to clean up redundant namespace declarations</li>
95 <li>recover - try hard to parse through broken XML</li>
96 <li>remove_blank_text - discard blank text nodes between tags (best used
97 together with a DTD)</li>
98 <li>remove_comments - discard comments</li>
99 <li>remove_pis - discard processing instructions</li>
100 <li>strip_cdata - replace CDATA sections by normal text content (on by
102 <li>resolve_entities - replace entities by their text value (on by
104 <li>huge_tree - disable security restrictions and support very deep trees
105 and very long text content (only affects libxml2 2.7+)</li>
106 <li>compact - use compact storage for short text content (on by default)</li>
108 <p>Other keyword arguments:</p>
110 <li>encoding - override the document encoding</li>
111 <li>target - a parser target object that will receive the parse events
112 (see <a class="reference internal" href="#the-target-parser-interface">The target parser interface</a>)</li>
113 <li>schema - an XMLSchema to validate against (see <a class="reference external" href="validation.html#xmlschema">validation</a>)</li>
116 <div class="section" id="error-log">
118 <p>Parsers have an <tt class="docutils literal">error_log</tt> property that lists the errors and
119 warnings of the last parser run:</p>
120 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLParser</span><span class="p">()</span>
121 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">parser</span><span class="o">.</span><span class="n">error_log</span><span class="p">))</span>
122 <span class="go">0</span>
124 <span class="gp">>>> </span><span class="n">tree</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">"<root></b>"</span><span class="p">,</span> <span class="n">parser</span><span class="p">)</span>
125 <span class="gt">Traceback (most recent call last):</span>
126 <span class="c">...</span>
127 <span class="gr">lxml.etree.XMLSyntaxError: Opening and ending tag mismatch</span>: <span class="n">root line 1 and b, line 1, column 11</span>
129 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">parser</span><span class="o">.</span><span class="n">error_log</span><span class="p">))</span>
130 <span class="go">1</span>
132 <span class="gp">>>> </span><span class="n">error</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">error_log</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
133 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">error</span><span class="o">.</span><span class="n">message</span><span class="p">)</span>
134 <span class="go">Opening and ending tag mismatch: root line 1 and b</span>
135 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">error</span><span class="o">.</span><span class="n">line</span><span class="p">)</span>
136 <span class="go">1</span>
137 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">error</span><span class="o">.</span><span class="n">column</span><span class="p">)</span>
138 <span class="go">11</span>
140 <p>Each entry in the log has the following properties:</p>
142 <li><tt class="docutils literal">message</tt>: the message text</li>
143 <li><tt class="docutils literal">domain</tt>: the domain ID (see the lxml.etree.ErrorDomains class)</li>
144 <li><tt class="docutils literal">type</tt>: the message type ID (see the lxml.etree.ErrorTypes class)</li>
145 <li><tt class="docutils literal">level</tt>: the log level ID (see the lxml.etree.ErrorLevels class)</li>
146 <li><tt class="docutils literal">line</tt>: the line at which the message originated (if applicable)</li>
147 <li><tt class="docutils literal">column</tt>: the character column at which the message originated (if applicable)</li>
148 <li><tt class="docutils literal">filename</tt>: the name of the file in which the message originated (if applicable)</li>
150 <p>For convenience, there are also three properties that provide readable
151 names for the ID values:</p>
153 <li><tt class="docutils literal">domain_name</tt></li>
154 <li><tt class="docutils literal">type_name</tt></li>
155 <li><tt class="docutils literal">level_name</tt></li>
157 <p>To filter for a specific kind of message, use the different
158 <tt class="docutils literal"><span class="pre">filter_*()</span></tt> methods on the error log (see the
159 lxml.etree._ListErrorLog class).</p>
161 <div class="section" id="parsing-html">
162 <h2>Parsing HTML</h2>
163 <p>HTML parsing is similarly simple. The parsers have a <tt class="docutils literal">recover</tt>
164 keyword argument that the HTMLParser sets by default. It lets libxml2
165 try its best to return a valid HTML tree with all content it can
166 manage to parse. It will not raise an exception on parser errors.
167 You should use libxml2 version 2.6.21 or newer to take advantage of
169 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">broken_html</span> <span class="o">=</span> <span class="s">"<html><head><title>test<body><h1>page title</h3>"</span>
171 <span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">HTMLParser</span><span class="p">()</span>
172 <span class="gp">>>> </span><span class="n">tree</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">broken_html</span><span class="p">),</span> <span class="n">parser</span><span class="p">)</span>
174 <span class="gp">>>> </span><span class="n">result</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">getroot</span><span class="p">(),</span>
175 <span class="gp">... </span> <span class="n">pretty_print</span><span class="o">=</span><span class="bp">True</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s">"html"</span><span class="p">)</span>
176 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
177 <span class="go"><html></span>
178 <span class="go"> <head></span>
179 <span class="go"> <title>test</title></span>
180 <span class="go"> </head></span>
181 <span class="go"> <body></span>
182 <span class="go"> <h1>page title</h1></span>
183 <span class="go"> </body></span>
184 <span class="go"></html></span>
186 <p>Lxml has an HTML function, similar to the XML shortcut known from
188 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">html</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">HTML</span><span class="p">(</span><span class="n">broken_html</span><span class="p">)</span>
189 <span class="gp">>>> </span><span class="n">result</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">html</span><span class="p">,</span> <span class="n">pretty_print</span><span class="o">=</span><span class="bp">True</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s">"html"</span><span class="p">)</span>
190 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
191 <span class="go"><html></span>
192 <span class="go"> <head></span>
193 <span class="go"> <title>test</title></span>
194 <span class="go"> </head></span>
195 <span class="go"> <body></span>
196 <span class="go"> <h1>page title</h1></span>
197 <span class="go"> </body></span>
198 <span class="go"></html></span>
200 <p>The support for parsing broken HTML depends entirely on libxml2's recovery
201 algorithm. It is <em>not</em> the fault of lxml if you find documents that are so
202 heavily broken that the parser cannot handle them. There is also no guarantee
203 that the resulting tree will contain all data from the original document. The
204 parser may have to drop seriously broken parts when struggling to keep
205 parsing. Especially misplaced meta tags can suffer from this, which may lead
206 to encoding problems.</p>
207 <p>Note that the result is a valid HTML tree, but it may not be a
208 well-formed XML tree. For example, XML forbids double hyphens in
209 comments, which the HTML parser will happily accept in recovery mode.
210 Therefore, if your goal is to serialise an HTML document as an
211 XML/XHTML document after parsing, you may have to apply some manual
212 preprocessing first.</p>
213 <p>Also note that the HTML parser is meant to parse HTML documents. For
214 XHTML documents, use the XML parser, which is namespace aware.</p>
216 <div class="section" id="doctype-information">
217 <h2>Doctype information</h2>
218 <p>The use of the libxml2 parsers makes some additional information available at
219 the API level. Currently, ElementTree objects can access the DOCTYPE
220 information provided by a parsed document, as well as the XML version and the
221 original encoding:</p>
222 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">pub_id</span> <span class="o">=</span> <span class="s">"-//W3C//DTD XHTML 1.0 Transitional//EN"</span>
223 <span class="gp">>>> </span><span class="n">sys_url</span> <span class="o">=</span> <span class="s">"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"</span>
224 <span class="gp">>>> </span><span class="n">doctype_string</span> <span class="o">=</span> <span class="s">'<!DOCTYPE html PUBLIC "</span><span class="si">%s</span><span class="s">" "</span><span class="si">%s</span><span class="s">">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">pub_id</span><span class="p">,</span> <span class="n">sys_url</span><span class="p">)</span>
225 <span class="gp">>>> </span><span class="n">xml_header</span> <span class="o">=</span> <span class="s">'<?xml version="1.0" encoding="ascii"?>'</span>
226 <span class="gp">>>> </span><span class="n">xhtml</span> <span class="o">=</span> <span class="n">xml_header</span> <span class="o">+</span> <span class="n">doctype_string</span> <span class="o">+</span> <span class="s">'<html><body></body></html>'</span>
228 <span class="gp">>>> </span><span class="n">tree</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xhtml</span><span class="p">))</span>
229 <span class="gp">>>> </span><span class="n">docinfo</span> <span class="o">=</span> <span class="n">tree</span><span class="o">.</span><span class="n">docinfo</span>
230 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">docinfo</span><span class="o">.</span><span class="n">public_id</span><span class="p">)</span>
231 <span class="go">-//W3C//DTD XHTML 1.0 Transitional//EN</span>
232 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">docinfo</span><span class="o">.</span><span class="n">system_url</span><span class="p">)</span>
233 <span class="go">http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd</span>
234 <span class="gp">>>> </span><span class="n">docinfo</span><span class="o">.</span><span class="n">doctype</span> <span class="o">==</span> <span class="n">doctype_string</span>
235 <span class="go">True</span>
237 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">docinfo</span><span class="o">.</span><span class="n">xml_version</span><span class="p">)</span>
238 <span class="go">1.0</span>
239 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">docinfo</span><span class="o">.</span><span class="n">encoding</span><span class="p">)</span>
240 <span class="go">ascii</span>
244 <div class="section" id="the-target-parser-interface">
245 <h1>The target parser interface</h1>
246 <p><a class="reference external" href="http://effbot.org/elementtree/elementtree-xmlparser.htm">As in ElementTree</a>, and similar to a SAX event handler, you can pass
247 a target object to the parser:</p>
248 <div class="syntax"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">EchoTarget</span><span class="p">:</span>
249 <span class="gp">... </span> <span class="k">def</span> <span class="nf">start</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">tag</span><span class="p">,</span> <span class="n">attrib</span><span class="p">):</span>
250 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"start </span><span class="si">%s</span><span class="s"> </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">tag</span><span class="p">,</span> <span class="n">attrib</span><span class="p">))</span>
251 <span class="gp">... </span> <span class="k">def</span> <span class="nf">end</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">tag</span><span class="p">):</span>
252 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"end </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="n">tag</span><span class="p">)</span>
253 <span class="gp">... </span> <span class="k">def</span> <span class="nf">data</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
254 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"data </span><span class="si">%r</span><span class="s">"</span> <span class="o">%</span> <span class="n">data</span><span class="p">)</span>
255 <span class="gp">... </span> <span class="k">def</span> <span class="nf">comment</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">text</span><span class="p">):</span>
256 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"comment </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="n">text</span><span class="p">)</span>
257 <span class="gp">... </span> <span class="k">def</span> <span class="nf">close</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
258 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"close"</span><span class="p">)</span>
259 <span class="gp">... </span> <span class="k">return</span> <span class="s">"closed!"</span>
261 <span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLParser</span><span class="p">(</span><span class="n">target</span> <span class="o">=</span> <span class="n">EchoTarget</span><span class="p">())</span>
263 <span class="gp">>>> </span><span class="n">result</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">"<element>some<!--comment-->text</element>"</span><span class="p">,</span>
264 <span class="gp">... </span> <span class="n">parser</span><span class="p">)</span>
265 <span class="go">start element {}</span>
266 <span class="go">data u'some'</span>
267 <span class="go">comment comment</span>
268 <span class="go">data u'text'</span>
269 <span class="go">end element</span>
270 <span class="go">close</span>
272 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
273 <span class="go">closed!</span>
275 <p>It is important for the <tt class="docutils literal">.close()</tt> method to reset the parser target
276 to a usable state, so that you can reuse the parser as often as you
278 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">result</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">"<element>some<!--comment-->text</element>"</span><span class="p">,</span>
279 <span class="gp">... </span> <span class="n">parser</span><span class="p">)</span>
280 <span class="go">start element {}</span>
281 <span class="go">data u'some'</span>
282 <span class="go">comment comment</span>
283 <span class="go">data u'text'</span>
284 <span class="go">end element</span>
285 <span class="go">close</span>
287 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
288 <span class="go">closed!</span>
290 <p>Starting with lxml 2.3, the <tt class="docutils literal">.close()</tt> method will also be called in
291 the error case. This diverges from the behaviour of ElementTree, but
292 allows target objects to clean up their state in all situations, so
293 that the parser can reuse them afterwards.</p>
294 <div class="syntax"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">CollectorTarget</span><span class="p">:</span>
295 <span class="gp">... </span> <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
296 <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">events</span> <span class="o">=</span> <span class="p">[]</span>
297 <span class="gp">... </span> <span class="k">def</span> <span class="nf">start</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">tag</span><span class="p">,</span> <span class="n">attrib</span><span class="p">):</span>
298 <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">events</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s">"start </span><span class="si">%s</span><span class="s"> </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">tag</span><span class="p">,</span> <span class="n">attrib</span><span class="p">))</span>
299 <span class="gp">... </span> <span class="k">def</span> <span class="nf">end</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">tag</span><span class="p">):</span>
300 <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">events</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s">"end </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="n">tag</span><span class="p">)</span>
301 <span class="gp">... </span> <span class="k">def</span> <span class="nf">data</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
302 <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">events</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s">"data </span><span class="si">%r</span><span class="s">"</span> <span class="o">%</span> <span class="n">data</span><span class="p">)</span>
303 <span class="gp">... </span> <span class="k">def</span> <span class="nf">comment</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">text</span><span class="p">):</span>
304 <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">events</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s">"comment </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="n">text</span><span class="p">)</span>
305 <span class="gp">... </span> <span class="k">def</span> <span class="nf">close</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
306 <span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">events</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s">"close"</span><span class="p">)</span>
307 <span class="gp">... </span> <span class="k">return</span> <span class="s">"closed!"</span>
309 <span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLParser</span><span class="p">(</span><span class="n">target</span> <span class="o">=</span> <span class="n">CollectorTarget</span><span class="p">())</span>
311 <span class="gp">>>> </span><span class="n">result</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">"<element>some</error>"</span><span class="p">,</span>
312 <span class="gp">... </span> <span class="n">parser</span><span class="p">)</span> <span class="c"># doctest: +ELLIPSIS</span>
313 <span class="gt">Traceback (most recent call last):</span>
314 <span class="c">...</span>
315 <span class="gr">lxml.etree.XMLSyntaxError</span>: <span class="n">Opening and ending tag mismatch...</span>
317 <span class="gp">>>> </span><span class="k">for</span> <span class="n">event</span> <span class="ow">in</span> <span class="n">parser</span><span class="o">.</span><span class="n">target</span><span class="o">.</span><span class="n">events</span><span class="p">:</span>
318 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="n">event</span><span class="p">)</span>
319 <span class="go">start element {}</span>
320 <span class="go">data u'some'</span>
321 <span class="go">close</span>
323 <p>Note that the parser does <em>not</em> build a tree when using a parser
324 target. The result of the parser run is whatever the target object
325 returns from its <tt class="docutils literal">.close()</tt> method. If you want to return an XML
326 tree here, you have to create it programmatically in the target
327 object. An example for a parser target that builds a tree is the
328 <tt class="docutils literal">TreeBuilder</tt>:</p>
329 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLParser</span><span class="p">(</span><span class="n">target</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">TreeBuilder</span><span class="p">())</span>
331 <span class="gp">>>> </span><span class="n">result</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">"<element>some<!--comment-->text</element>"</span><span class="p">,</span>
332 <span class="gp">... </span> <span class="n">parser</span><span class="p">)</span>
334 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
335 <span class="go">element</span>
336 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">text</span><span class="p">)</span>
337 <span class="go">comment</span>
340 <div class="section" id="the-feed-parser-interface">
341 <h1>The feed parser interface</h1>
342 <p>Since lxml 2.0, the parsers have a feed parser interface that is
343 compatible to the <a class="reference external" href="http://effbot.org/elementtree/elementtree-xmlparser.htm">ElementTree parsers</a>. You can use it to feed data
344 into the parser in a controlled step-by-step way.</p>
345 <p>In lxml.etree, you can use both interfaces to a parser at the same
346 time: the <tt class="docutils literal">parse()</tt> or <tt class="docutils literal">XML()</tt> functions, and the feed parser
347 interface. Both are independent and will not conflict (except if used
348 in conjunction with a parser target object as described above).</p>
349 <p>To start parsing with a feed parser, just call its <tt class="docutils literal">feed()</tt> method
350 to feed it some data.</p>
351 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLParser</span><span class="p">()</span>
353 <span class="gp">>>> </span><span class="k">for</span> <span class="n">data</span> <span class="ow">in</span> <span class="p">(</span><span class="s">'<?xml versio'</span><span class="p">,</span> <span class="s">'n="1.0"?'</span><span class="p">,</span> <span class="s">'><roo'</span><span class="p">,</span> <span class="s">'t><a'</span><span class="p">,</span> <span class="s">'/></root>'</span><span class="p">):</span>
354 <span class="gp">... </span> <span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
356 <p>When you are done parsing, you <strong>must</strong> call the <tt class="docutils literal">close()</tt> method to
357 retrieve the root Element of the parse result document, and to unlock the
359 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
361 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
362 <span class="go">root</span>
363 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">root</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
364 <span class="go">a</span>
366 <p>If you do not call <tt class="docutils literal">close()</tt>, the parser will stay locked and
367 subsequent feeds will keep appending data, usually resulting in a non
368 well-formed document and an unexpected parser error. So make sure you
369 always close the parser after use, also in the exception case.</p>
370 <p>Another way of achieving the same step-by-step parsing is by writing your own
371 file-like object that returns a chunk of data on each <tt class="docutils literal">read()</tt> call. Where
372 the feed parser interface allows you to actively pass data chunks into the
373 parser, a file-like object passively responds to <tt class="docutils literal">read()</tt> requests of the
374 parser itself. Depending on the data source, either way may be more natural.</p>
375 <p>Note that the feed parser has its own error log called
376 <tt class="docutils literal">feed_error_log</tt>. Errors in the feed parser do not show up in the
377 normal <tt class="docutils literal">error_log</tt> and vice versa.</p>
378 <p>You can also combine the feed parser interface with the target parser:</p>
379 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLParser</span><span class="p">(</span><span class="n">target</span> <span class="o">=</span> <span class="n">EchoTarget</span><span class="p">())</span>
381 <span class="gp">>>> </span><span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="s">"<eleme"</span><span class="p">)</span>
382 <span class="gp">>>> </span><span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="s">"nt>some text</elem"</span><span class="p">)</span>
383 <span class="go">start element {}</span>
384 <span class="go">data u'some text'</span>
385 <span class="gp">>>> </span><span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="s">"ent>"</span><span class="p">)</span>
386 <span class="go">end element</span>
388 <span class="gp">>>> </span><span class="n">result</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
389 <span class="go">close</span>
390 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
391 <span class="go">closed!</span>
393 <p>Again, this prevents the automatic creation of an XML tree and leaves
394 all the event handling to the target object. The <tt class="docutils literal">close()</tt> method
395 of the parser forwards the return value of the target's <tt class="docutils literal">close()</tt>
398 <div class="section" id="iterparse-and-iterwalk">
399 <h1>iterparse and iterwalk</h1>
400 <p>As known from ElementTree, the <tt class="docutils literal">iterparse()</tt> utility function
401 returns an iterator that generates parser events for an XML file (or
402 file-like object), while building the tree. The values are tuples
403 <tt class="docutils literal"><span class="pre">(event-type,</span> object)</tt>. The event types supported by ElementTree
404 and lxml.etree are the strings 'start', 'end', 'start-ns' and
406 <p>The 'start' and 'end' events represent opening and closing elements.
407 They are accompanied by the respective Element instance. By default,
408 only 'end' events are generated:</p>
409 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">xml</span> <span class="o">=</span> <span class="s">'''</span><span class="se">\</span>
410 <span class="gp">... </span><span class="s"><root></span>
411 <span class="gp">... </span><span class="s"> <element key='value'>text</element></span>
412 <span class="gp">... </span><span class="s"> <element>text</element>tail</span>
413 <span class="gp">... </span><span class="s"> <empty-element xmlns="http://testns/" /></span>
414 <span class="gp">... </span><span class="s"></root></span>
415 <span class="gp">... </span><span class="s">'''</span>
417 <span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">))</span>
418 <span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
419 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
420 <span class="go">end: element</span>
421 <span class="go">end: element</span>
422 <span class="go">end: {http://testns/}empty-element</span>
423 <span class="go">end: root</span>
425 <p>The resulting tree is available through the <tt class="docutils literal">root</tt> property of the iterator:</p>
426 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">context</span><span class="o">.</span><span class="n">root</span><span class="o">.</span><span class="n">tag</span>
427 <span class="go">'root'</span>
429 <p>The other event types can be activated with the <tt class="docutils literal">events</tt> keyword argument:</p>
430 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">events</span> <span class="o">=</span> <span class="p">(</span><span class="s">"start"</span><span class="p">,</span> <span class="s">"end"</span><span class="p">)</span>
431 <span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">),</span> <span class="n">events</span><span class="o">=</span><span class="n">events</span><span class="p">)</span>
432 <span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
433 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
434 <span class="go">start: root</span>
435 <span class="go">start: element</span>
436 <span class="go">end: element</span>
437 <span class="go">start: element</span>
438 <span class="go">end: element</span>
439 <span class="go">start: {http://testns/}empty-element</span>
440 <span class="go">end: {http://testns/}empty-element</span>
441 <span class="go">end: root</span>
443 <p>The 'start-ns' and 'end-ns' events notify about namespace
444 declarations. They do not come with Elements. Instead, the value of
445 the 'start-ns' event is a tuple <tt class="docutils literal">(prefix, namespaceURI)</tt> that
446 designates the beginning of a prefix-namespace mapping. The
447 corresponding <tt class="docutils literal"><span class="pre">end-ns</span></tt> event does not have a value (None). It is
448 common practice to use a list as namespace stack and pop the last
449 entry on the 'end-ns' event.</p>
450 <div class="syntax"><pre><span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">xml</span><span class="p">[:</span><span class="o">-</span><span class="mi">1</span><span class="p">])</span>
451 <span class="go"><root></span>
452 <span class="go"> <element key='value'>text</element></span>
453 <span class="go"> <element>text</element>tail</span>
454 <span class="go"> <empty-element xmlns="http://testns/" /></span>
455 <span class="go"></root></span>
457 <span class="gp">>>> </span><span class="n">events</span> <span class="o">=</span> <span class="p">(</span><span class="s">"start"</span><span class="p">,</span> <span class="s">"end"</span><span class="p">,</span> <span class="s">"start-ns"</span><span class="p">,</span> <span class="s">"end-ns"</span><span class="p">)</span>
458 <span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">),</span> <span class="n">events</span><span class="o">=</span><span class="n">events</span><span class="p">)</span>
459 <span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
460 <span class="gp">... </span> <span class="k">if</span> <span class="n">action</span> <span class="ow">in</span> <span class="p">(</span><span class="s">'start'</span><span class="p">,</span> <span class="s">'end'</span><span class="p">):</span>
461 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
462 <span class="gp">... </span> <span class="k">elif</span> <span class="n">action</span> <span class="o">==</span> <span class="s">'start-ns'</span><span class="p">:</span>
463 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="p">))</span>
464 <span class="gp">... </span> <span class="k">else</span><span class="p">:</span>
465 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="n">action</span><span class="p">)</span>
466 <span class="go">start: root</span>
467 <span class="go">start: element</span>
468 <span class="go">end: element</span>
469 <span class="go">start: element</span>
470 <span class="go">end: element</span>
471 <span class="go">start-ns: ('', 'http://testns/')</span>
472 <span class="go">start: {http://testns/}empty-element</span>
473 <span class="go">end: {http://testns/}empty-element</span>
474 <span class="go">end-ns</span>
475 <span class="go">end: root</span>
477 <div class="section" id="selective-tag-events">
478 <h2>Selective tag events</h2>
479 <p>As an extension over ElementTree, lxml.etree accepts a <tt class="docutils literal">tag</tt> keyword
480 argument just like <tt class="docutils literal">element.iter(tag)</tt>. This restricts events to a
481 specific tag or namespace:</p>
482 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">),</span> <span class="n">tag</span><span class="o">=</span><span class="s">"element"</span><span class="p">)</span>
483 <span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
484 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
485 <span class="go">end: element</span>
486 <span class="go">end: element</span>
488 <span class="gp">>>> </span><span class="n">events</span> <span class="o">=</span> <span class="p">(</span><span class="s">"start"</span><span class="p">,</span> <span class="s">"end"</span><span class="p">)</span>
489 <span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span>
490 <span class="gp">... </span> <span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">),</span> <span class="n">events</span><span class="o">=</span><span class="n">events</span><span class="p">,</span> <span class="n">tag</span><span class="o">=</span><span class="s">"{http://testns/}*"</span><span class="p">)</span>
491 <span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
492 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
493 <span class="go">start: {http://testns/}empty-element</span>
494 <span class="go">end: {http://testns/}empty-element</span>
497 <div class="section" id="comments-and-pis">
498 <h2>Comments and PIs</h2>
499 <p>As an extension over ElementTree, the <tt class="docutils literal">iterparse()</tt> function in
500 lxml.etree also supports the event types 'comment' and 'pi' for the
501 respective XML structures.</p>
502 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">commented_xml</span> <span class="o">=</span> <span class="s">'''</span><span class="se">\</span>
503 <span class="gp">... </span><span class="s"><?some pi ?></span>
504 <span class="gp">... </span><span class="s"><!-- a comment --></span>
505 <span class="gp">... </span><span class="s"><root></span>
506 <span class="gp">... </span><span class="s"> <element key='value'>text</element></span>
507 <span class="gp">... </span><span class="s"> <!-- another comment --></span>
508 <span class="gp">... </span><span class="s"> <element>text</element>tail</span>
509 <span class="gp">... </span><span class="s"> <empty-element xmlns="http://testns/" /></span>
510 <span class="gp">... </span><span class="s"></root></span>
511 <span class="gp">... </span><span class="s">'''</span>
513 <span class="gp">>>> </span><span class="n">events</span> <span class="o">=</span> <span class="p">(</span><span class="s">"start"</span><span class="p">,</span> <span class="s">"end"</span><span class="p">,</span> <span class="s">"comment"</span><span class="p">,</span> <span class="s">"pi"</span><span class="p">)</span>
514 <span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">commented_xml</span><span class="p">),</span> <span class="n">events</span><span class="o">=</span><span class="n">events</span><span class="p">)</span>
515 <span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
516 <span class="gp">... </span> <span class="k">if</span> <span class="n">action</span> <span class="ow">in</span> <span class="p">(</span><span class="s">'start'</span><span class="p">,</span> <span class="s">'end'</span><span class="p">):</span>
517 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
518 <span class="gp">... </span> <span class="k">elif</span> <span class="n">action</span> <span class="o">==</span> <span class="s">'pi'</span><span class="p">:</span>
519 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: -</span><span class="si">%s</span><span class="s">=</span><span class="si">%s</span><span class="s">-"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">target</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">text</span><span class="p">))</span>
520 <span class="gp">... </span> <span class="k">else</span><span class="p">:</span> <span class="c"># 'comment'</span>
521 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: -</span><span class="si">%s</span><span class="s">-"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">text</span><span class="p">))</span>
522 <span class="go">pi: -some=pi -</span>
523 <span class="go">comment: - a comment -</span>
524 <span class="go">start: root</span>
525 <span class="go">start: element</span>
526 <span class="go">end: element</span>
527 <span class="go">comment: - another comment -</span>
528 <span class="go">start: element</span>
529 <span class="go">end: element</span>
530 <span class="go">start: {http://testns/}empty-element</span>
531 <span class="go">end: {http://testns/}empty-element</span>
532 <span class="go">end: root</span>
534 <span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">context</span><span class="o">.</span><span class="n">root</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
535 <span class="go">root</span>
538 <div class="section" id="modifying-the-tree">
539 <h2>Modifying the tree</h2>
540 <p>You can modify the element and its descendants when handling the 'end' event.
541 To save memory, for example, you can remove subtrees that are no longer
543 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">))</span>
544 <span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
545 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">elem</span><span class="p">))</span>
546 <span class="gp">... </span> <span class="n">elem</span><span class="o">.</span><span class="n">clear</span><span class="p">()</span>
547 <span class="go">0</span>
548 <span class="go">0</span>
549 <span class="go">0</span>
550 <span class="go">3</span>
551 <span class="gp">>>> </span><span class="n">context</span><span class="o">.</span><span class="n">root</span><span class="o">.</span><span class="n">getchildren</span><span class="p">()</span>
552 <span class="go">[]</span>
554 <p><strong>WARNING</strong>: During the 'start' event, any content of the element,
555 such as the descendants, following siblings or text, is not yet
556 available and should not be accessed. Only attributes are guaranteed
557 to be set. During the 'end' event, the element and its descendants
558 can be freely modified, but its following siblings should not be
559 accessed. During either of the two events, you <strong>must not</strong> modify or
560 move the ancestors (parents) of the current element. You should also
561 avoid moving or discarding the element itself. The golden rule is: do
562 not touch anything that will have to be touched again by the parser
564 <p>If you have elements with a long list of children in your XML file and want to
565 save more memory during parsing, you can clean up the preceding siblings of
566 the current element:</p>
567 <div class="syntax"><pre><span class="gp">>>> </span><span class="k">for</span> <span class="n">event</span><span class="p">,</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">)):</span>
568 <span class="gp">... </span> <span class="c"># ... do something with the element</span>
569 <span class="gp">... </span> <span class="n">element</span><span class="o">.</span><span class="n">clear</span><span class="p">()</span> <span class="c"># clean up children</span>
570 <span class="gp">... </span> <span class="k">while</span> <span class="n">element</span><span class="o">.</span><span class="n">getprevious</span><span class="p">()</span> <span class="ow">is</span> <span class="ow">not</span> <span class="bp">None</span><span class="p">:</span>
571 <span class="gp">... </span> <span class="k">del</span> <span class="n">element</span><span class="o">.</span><span class="n">getparent</span><span class="p">()[</span><span class="mi">0</span><span class="p">]</span> <span class="c"># clean up preceding siblings</span>
573 <p>The <tt class="docutils literal">while</tt> loop deletes multiple siblings in a row. This is only necessary
574 if you skipped over some of them using the <tt class="docutils literal">tag</tt> keyword argument.
575 Otherwise, a simple <tt class="docutils literal">if</tt> should do. The more selective your tag is,
576 however, the more thought you will have to put into finding the right way to
577 clean up the elements that were skipped. Therefore, it is sometimes easier to
578 traverse all elements and do the tag selection by hand in the event handler
581 <div class="section" id="iterwalk">
583 <p>A second extension over ElementTree is the <tt class="docutils literal">iterwalk()</tt> function. It
584 behaves exactly like <tt class="docutils literal">iterparse()</tt>, but works on Elements and ElementTrees:</p>
585 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="n">xml</span><span class="p">)</span>
586 <span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterwalk</span><span class="p">(</span>
587 <span class="gp">... </span> <span class="n">root</span><span class="p">,</span> <span class="n">events</span><span class="o">=</span><span class="p">(</span><span class="s">"start"</span><span class="p">,</span> <span class="s">"end"</span><span class="p">),</span> <span class="n">tag</span><span class="o">=</span><span class="s">"element"</span><span class="p">)</span>
588 <span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
589 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
590 <span class="go">start: element</span>
591 <span class="go">end: element</span>
592 <span class="go">start: element</span>
593 <span class="go">end: element</span>
595 <span class="gp">>>> </span><span class="n">f</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">)</span>
596 <span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span>
597 <span class="gp">... </span> <span class="n">f</span><span class="p">,</span> <span class="n">events</span><span class="o">=</span><span class="p">(</span><span class="s">"start"</span><span class="p">,</span> <span class="s">"end"</span><span class="p">),</span> <span class="n">tag</span><span class="o">=</span><span class="s">"element"</span><span class="p">)</span>
599 <span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
600 <span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
601 <span class="go">start: element</span>
602 <span class="go">end: element</span>
603 <span class="go">start: element</span>
604 <span class="go">end: element</span>
608 <div class="section" id="python-unicode-strings">
609 <h1>Python unicode strings</h1>
610 <p>lxml.etree has broader support for Python unicode strings than the ElementTree
611 library. First of all, where ElementTree would raise an exception, the
612 parsers in lxml.etree can handle unicode strings straight away. This is most
613 helpful for XML snippets embedded in source code using the <tt class="docutils literal">XML()</tt>
615 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">uxml</span> <span class="o">=</span> <span class="s">u'<test> </span><span class="se">\uf8d1</span><span class="s"> + </span><span class="se">\uf8d2</span><span class="s"> </test>'</span>
616 <span class="gp">>>> </span><span class="n">uxml</span>
617 <span class="go">u'<test> \uf8d1 + \uf8d2 </test>'</span>
618 <span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="n">uxml</span><span class="p">)</span>
620 <p>This requires, however, that unicode strings do not specify a conflicting
621 encoding themselves and thus lie about their real encoding:</p>
622 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span> <span class="s">u'<?xml version="1.0" encoding="ASCII"?></span><span class="se">\n</span><span class="s">'</span> <span class="o">+</span> <span class="n">uxml</span> <span class="p">)</span>
623 <span class="gt">Traceback (most recent call last):</span>
624 <span class="c">...</span>
625 <span class="gr">ValueError</span>: <span class="n">Unicode strings with encoding declaration are not supported.</span>
627 <p>Similarly, you will get errors when you try the same with HTML data in a
628 unicode string that specifies a charset in a meta tag of the header. You
629 should generally avoid converting XML/HTML data to unicode before passing it
630 into the parsers. It is both slower and error prone.</p>
631 <div class="section" id="serialising-to-unicode-strings">
632 <h2>Serialising to Unicode strings</h2>
633 <p>To serialize the result, you would normally use the <tt class="docutils literal">tostring()</tt>
634 module function, which serializes to plain ASCII by default or a
635 number of other byte encodings if asked for:</p>
636 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
637 <span class="go">b'<test> &#63697; + &#63698; </test>'</span>
639 <span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="s">'UTF-8'</span><span class="p">,</span> <span class="n">xml_declaration</span><span class="o">=</span><span class="bp">False</span><span class="p">)</span>
640 <span class="go">b'<test> \xef\xa3\x91 + \xef\xa3\x92 </test>'</span>
642 <p>As an extension, lxml.etree recognises the unicode type as an argument to the
643 encoding parameter to build a Python unicode representation of a tree:</p>
644 <div class="syntax"><pre><span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="nb">unicode</span><span class="p">)</span>
645 <span class="go">u'<test> \uf8d1 + \uf8d2 </test>'</span>
647 <span class="gp">>>> </span><span class="n">el</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Element</span><span class="p">(</span><span class="s">"test"</span><span class="p">)</span>
648 <span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">el</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="nb">unicode</span><span class="p">)</span>
649 <span class="go">u'<test/>'</span>
651 <span class="gp">>>> </span><span class="n">subel</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">SubElement</span><span class="p">(</span><span class="n">el</span><span class="p">,</span> <span class="s">"subtest"</span><span class="p">)</span>
652 <span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">el</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="nb">unicode</span><span class="p">)</span>
653 <span class="go">u'<test><subtest/></test>'</span>
655 <span class="gp">>>> </span><span class="n">tree</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">ElementTree</span><span class="p">(</span><span class="n">el</span><span class="p">)</span>
656 <span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">tree</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="nb">unicode</span><span class="p">)</span>
657 <span class="go">u'<test><subtest/></test>'</span>
659 <p>The result of <tt class="docutils literal">tostring(encoding=unicode)</tt> can be treated like any
660 other Python unicode string and then passed back into the parsers.
661 However, if you want to save the result to a file or pass it over the
662 network, you should use <tt class="docutils literal">write()</tt> or <tt class="docutils literal">tostring()</tt> with a byte
663 encoding (typically UTF-8) to serialize the XML. The main reason is
664 that unicode strings returned by <tt class="docutils literal">tostring(encoding=unicode)</tt> are
665 not byte streams and they never have an XML declaration to specify
666 their encoding. These strings are most likely not parsable by other
668 <p>For normal byte encodings, the <tt class="docutils literal">tostring()</tt> function automatically
669 adds a declaration as needed that reflects the encoding of the
670 returned string. This makes it possible for other parsers to
671 correctly parse the XML byte stream. Note that using <tt class="docutils literal">tostring()</tt>
672 with UTF-8 is also considerably faster in most cases.</p>
677 <hr class="footer" />
678 Generated on: 2012-07-31.
projects / platform / upstream / python-lxml.git / blob