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<h2 class="title"><a name="kgp.search"></a>9.5. Searching for elements
</h2>
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<div class="abstract">
<p>Traversing <span class="acronym">XML</span> documents by stepping through each node can be tedious. If you're looking for something in particular, buried deep within
your <span class="acronym">XML</span> document, there is a shortcut you can use to find it quickly: <tt class="function">getElementsByTagName</tt>.
</p>
</div>
<p>For this section, you'll be using the <tt class="filename">binary.xml</tt> grammar file, which looks like this:
</p>
<div class="example"><a name="d0e24431"></a><h3 class="title">Example 9.20. <tt class="filename">binary.xml</tt></h3><pre class="screen"><span class="computeroutput"><?xml version="1.0"?>
<!DOCTYPE grammar PUBLIC "-//diveintopython.org//DTD Kant Generator Pro v1.0//EN" "kgp.dtd">
<grammar>
<ref id="bit">
<p>0</p>
<p>1</p>
</ref>
<ref id="byte">
<p><xref id="bit"/><xref id="bit"/><xref id="bit"/><xref id="bit"/>\
<xref id="bit"/><xref id="bit"/><xref id="bit"/><xref id="bit"/></p>
</ref>
</grammar></span></pre></div>
<p>It has two <tt class="sgmltag-element">ref</tt>s, <tt class="literal">'bit'</tt> and <tt class="literal">'byte'</tt>. A <tt class="literal">bit</tt> is either a <tt class="literal">'0'</tt> or <tt class="literal">'1'</tt>, and a <tt class="literal">byte</tt> is 8 <tt class="literal">bit</tt>s.
</p>
<div class="example"><a name="d0e24464"></a><h3 class="title">Example 9.21. Introducing <tt class="function">getElementsByTagName</tt></h3><pre class="screen">
<tt class="prompt">>>> </tt><span class="userinput"><span class='pykeyword'>from</span> xml.dom <span class='pykeyword'>import</span> minidom</span>
<tt class="prompt">>>> </tt><span class="userinput">xmldoc = minidom.parse(<span class='pystring'>'binary.xml'</span>)</span>
<tt class="prompt">>>> </tt><span class="userinput">reflist = xmldoc.getElementsByTagName(<span class='pystring'>'ref'</span>)</span> <a name="kgp.search.1.1"></a><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12">
<tt class="prompt">>>> </tt><span class="userinput">reflist</span>
<span class="computeroutput">[<DOM Element: ref at 136138108>, <DOM Element: ref at 136144292>]</span>
<tt class="prompt">>>> </tt><span class="userinput"><span class='pykeyword'>print</span> reflist[0].toxml()</span>
<span class="computeroutput"><ref id="bit">
<p>0</p>
<p>1</p>
</ref></span>
<tt class="prompt">>>> </tt><span class="userinput"><span class='pykeyword'>print</span> reflist[1].toxml()</span>
<span class="computeroutput"><ref id="byte">
<p><xref id="bit"/><xref id="bit"/><xref id="bit"/><xref id="bit"/>\
<xref id="bit"/><xref id="bit"/><xref id="bit"/><xref id="bit"/></p>
</ref>
</span></pre><div class="calloutlist">
<table border="0" summary="Callout list">
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<td width="12" valign="top" align="left"><a href="#kgp.search.1.1"><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left"><tt class="function">getElementsByTagName</tt> takes one argument, the name of the element you wish to find. It returns a list of <tt class="classname">Element</tt> objects, corresponding to the <span class="acronym">XML</span> elements that have that name. In this case, you find two <tt class="literal">ref</tt> elements.
</td>
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<div class="example"><a name="d0e24526"></a><h3 class="title">Example 9.22. Every element is searchable</h3><pre class="screen">
<tt class="prompt">>>> </tt><span class="userinput">firstref = reflist[0]</span> <a name="kgp.search.2.1"></a><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12">
<tt class="prompt">>>> </tt><span class="userinput"><span class='pykeyword'>print</span> firstref.toxml()</span>
<span class="computeroutput"><ref id="bit">
<p>0</p>
<p>1</p>
</ref></span>
<tt class="prompt">>>> </tt><span class="userinput">plist = firstref.getElementsByTagName(<span class='pystring'>"p"</span>)</span> <a name="kgp.search.2.2"></a><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12">
<tt class="prompt">>>> </tt><span class="userinput">plist</span>
<span class="computeroutput">[<DOM Element: p at 136140116>, <DOM Element: p at 136142172>]</span>
<tt class="prompt">>>> </tt><span class="userinput"><span class='pykeyword'>print</span> plist[0].toxml()</span> <a name="kgp.search.2.3"></a><img src="../images/callouts/3.png" alt="3" border="0" width="12" height="12">
<span class="computeroutput"><p>0</p></span>
<tt class="prompt">>>> </tt><span class="userinput"><span class='pykeyword'>print</span> plist[1].toxml()</span>
<span class="computeroutput"><p>1</p></span></pre><div class="calloutlist">
<table border="0" summary="Callout list">
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<td width="12" valign="top" align="left"><a href="#kgp.search.2.1"><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">Continuing from the previous example, the first object in your <tt class="varname">reflist</tt> is the <tt class="literal">'bit'</tt> <tt class="sgmltag-element">ref</tt> element.
</td>
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<td width="12" valign="top" align="left"><a href="#kgp.search.2.2"><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">You can use the same <tt class="function">getElementsByTagName</tt> method on this <tt class="classname">Element</tt> to find all the <tt class="sgmltag-element"><p></tt> elements within the <tt class="literal">'bit'</tt> <tt class="sgmltag-element">ref</tt> element.
</td>
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<td width="12" valign="top" align="left"><a href="#kgp.search.2.3"><img src="../images/callouts/3.png" alt="3" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">Just as before, the <tt class="function">getElementsByTagName</tt> method returns a list of all the elements it found. In this case, you have two, one for each bit.
</td>
</tr>
</table>
</div>
</div>
<div class="example"><a name="d0e24615"></a><h3 class="title">Example 9.23. Searching is actually recursive</h3><pre class="screen">
<tt class="prompt">>>> </tt><span class="userinput">plist = xmldoc.getElementsByTagName(<span class='pystring'>"p"</span>)</span> <a name="kgp.search.3.1"></a><img src="../images/callouts/1.png" alt="1" border="0" width="12" height="12">
<tt class="prompt">>>> </tt><span class="userinput">plist</span>
<span class="computeroutput">[<DOM Element: p at 136140116>, <DOM Element: p at 136142172>, <DOM Element: p at 136146124>]</span>
<tt class="prompt">>>> </tt><span class="userinput">plist[0].toxml()</span> <a name="kgp.search.3.2"></a><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12">
<span class="computeroutput">'<p>0</p>'</span>
<tt class="prompt">>>> </tt><span class="userinput">plist[1].toxml()</span>
<span class="computeroutput">'<p>1</p>'</span>
<tt class="prompt">>>> </tt><span class="userinput">plist[2].toxml()</span> <a name="kgp.search.3.3"></a><img src="../images/callouts/3.png" alt="3" border="0" width="12" height="12">
<span class="computeroutput">'<p><xref id="bit"/><xref id="bit"/><xref id="bit"/><xref id="bit"/>\
<xref id="bit"/><xref id="bit"/><xref id="bit"/><xref id="bit"/></p>'</span></pre><div class="calloutlist">
<table border="0" summary="Callout list">
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</td>
<td valign="top" align="left">Note carefully the difference between this and the previous example. Previously, you were searching for <tt class="sgmltag-element">p</tt> elements within <tt class="varname">firstref</tt>, but here you are searching for <tt class="sgmltag-element">p</tt> elements within <tt class="varname">xmldoc</tt>, the root-level object that represents the entire <span class="acronym">XML</span> document. This <span class="emphasis"><em>does</em></span> find the <tt class="sgmltag-element">p</tt> elements nested within the <tt class="sgmltag-element">ref</tt> elements within the root <tt class="sgmltag-element">grammar</tt> element.
</td>
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<td width="12" valign="top" align="left"><a href="#kgp.search.3.2"><img src="../images/callouts/2.png" alt="2" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">The first two <tt class="sgmltag-element">p</tt> elements are within the first <tt class="sgmltag-element">ref</tt> (the <tt class="literal">'bit'</tt> <tt class="sgmltag-element">ref</tt>).
</td>
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<td width="12" valign="top" align="left"><a href="#kgp.search.3.3"><img src="../images/callouts/3.png" alt="3" border="0" width="12" height="12"></a>
</td>
<td valign="top" align="left">The last <tt class="sgmltag-element">p</tt> element is the one within the second <tt class="sgmltag-element">ref</tt> (the <tt class="literal">'byte'</tt> <tt class="sgmltag-element">ref</tt>).
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