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<li><a class="reference internal" href="#">OrderedDict</a><ul>
<li><a class="reference internal" href="#equality">Equality</a></li>
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<div class="section" id="ordereddict">
<h1>OrderedDict<a class="headerlink" href="#ordereddict" title="Permalink to this headline">¶</a></h1>
<p>An <tt class="xref py py-class docutils literal"><span class="pre">OrderedDict</span></tt> is a dictionary subclass that remembers the
order in which its contents are added.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">collections</span>
<span class="k">print</span> <span class="s">'Regular dictionary:'</span>
<span class="n">d</span> <span class="o">=</span> <span class="p">{}</span>
<span class="n">d</span><span class="p">[</span><span class="s">'a'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'A'</span>
<span class="n">d</span><span class="p">[</span><span class="s">'b'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'B'</span>
<span class="n">d</span><span class="p">[</span><span class="s">'c'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'C'</span>
<span class="n">d</span><span class="p">[</span><span class="s">'d'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'D'</span>
<span class="n">d</span><span class="p">[</span><span class="s">'e'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'E'</span>
<span class="k">for</span> <span class="n">k</span><span class="p">,</span> <span class="n">v</span> <span class="ow">in</span> <span class="n">d</span><span class="o">.</span><span class="n">items</span><span class="p">():</span>
<span class="k">print</span> <span class="n">k</span><span class="p">,</span> <span class="n">v</span>
<span class="k">print</span> <span class="s">'</span><span class="se">\n</span><span class="s">OrderedDict:'</span>
<span class="n">d</span> <span class="o">=</span> <span class="n">collections</span><span class="o">.</span><span class="n">OrderedDict</span><span class="p">()</span>
<span class="n">d</span><span class="p">[</span><span class="s">'a'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'A'</span>
<span class="n">d</span><span class="p">[</span><span class="s">'b'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'B'</span>
<span class="n">d</span><span class="p">[</span><span class="s">'c'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'C'</span>
<span class="n">d</span><span class="p">[</span><span class="s">'d'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'D'</span>
<span class="n">d</span><span class="p">[</span><span class="s">'e'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'E'</span>
<span class="k">for</span> <span class="n">k</span><span class="p">,</span> <span class="n">v</span> <span class="ow">in</span> <span class="n">d</span><span class="o">.</span><span class="n">items</span><span class="p">():</span>
<span class="k">print</span> <span class="n">k</span><span class="p">,</span> <span class="n">v</span>
</pre></div>
</div>
<p>A regular <tt class="xref py py-class docutils literal"><span class="pre">dict</span></tt> does not track the insertion order, and
iterating over it produces the values in an arbitrary order. In an
<tt class="xref py py-class docutils literal"><span class="pre">OrderedDict</span></tt>, by contrast, the order the items are inserted is
remembered and used when creating an iterator.</p>
<div class="highlight-python"><pre>$ python collections_ordereddict_iter.py
Regular dictionary:
a A
c C
b B
e E
d D
OrderedDict:
a A
b B
c C
d D
e E</pre>
</div>
<div class="section" id="equality">
<h2>Equality<a class="headerlink" href="#equality" title="Permalink to this headline">¶</a></h2>
<p>A regular <tt class="xref py py-class docutils literal"><span class="pre">dict</span></tt> looks at its contents when testing for
equality. An <tt class="xref py py-class docutils literal"><span class="pre">OrderedDict</span></tt> also considers the order the items
were added.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">collections</span>
<span class="k">print</span> <span class="s">'dict :'</span><span class="p">,</span>
<span class="n">d1</span> <span class="o">=</span> <span class="p">{}</span>
<span class="n">d1</span><span class="p">[</span><span class="s">'a'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'A'</span>
<span class="n">d1</span><span class="p">[</span><span class="s">'b'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'B'</span>
<span class="n">d1</span><span class="p">[</span><span class="s">'c'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'C'</span>
<span class="n">d1</span><span class="p">[</span><span class="s">'d'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'D'</span>
<span class="n">d1</span><span class="p">[</span><span class="s">'e'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'E'</span>
<span class="n">d2</span> <span class="o">=</span> <span class="p">{}</span>
<span class="n">d2</span><span class="p">[</span><span class="s">'e'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'E'</span>
<span class="n">d2</span><span class="p">[</span><span class="s">'d'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'D'</span>
<span class="n">d2</span><span class="p">[</span><span class="s">'c'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'C'</span>
<span class="n">d2</span><span class="p">[</span><span class="s">'b'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'B'</span>
<span class="n">d2</span><span class="p">[</span><span class="s">'a'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'A'</span>
<span class="k">print</span> <span class="n">d1</span> <span class="o">==</span> <span class="n">d2</span>
<span class="k">print</span> <span class="s">'OrderedDict:'</span><span class="p">,</span>
<span class="n">d1</span> <span class="o">=</span> <span class="n">collections</span><span class="o">.</span><span class="n">OrderedDict</span><span class="p">()</span>
<span class="n">d1</span><span class="p">[</span><span class="s">'a'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'A'</span>
<span class="n">d1</span><span class="p">[</span><span class="s">'b'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'B'</span>
<span class="n">d1</span><span class="p">[</span><span class="s">'c'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'C'</span>
<span class="n">d1</span><span class="p">[</span><span class="s">'d'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'D'</span>
<span class="n">d1</span><span class="p">[</span><span class="s">'e'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'E'</span>
<span class="n">d2</span> <span class="o">=</span> <span class="n">collections</span><span class="o">.</span><span class="n">OrderedDict</span><span class="p">()</span>
<span class="n">d2</span><span class="p">[</span><span class="s">'e'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'E'</span>
<span class="n">d2</span><span class="p">[</span><span class="s">'d'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'D'</span>
<span class="n">d2</span><span class="p">[</span><span class="s">'c'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'C'</span>
<span class="n">d2</span><span class="p">[</span><span class="s">'b'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'B'</span>
<span class="n">d2</span><span class="p">[</span><span class="s">'a'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'A'</span>
<span class="k">print</span> <span class="n">d1</span> <span class="o">==</span> <span class="n">d2</span>
</pre></div>
</div>
<p>In this case, since the two ordered dictionaries are created from
values in a different order, they are considered to be different.</p>
<div class="highlight-python"><pre>$ python collections_ordereddict_equality.py
dict : True
OrderedDict: False</pre>
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