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<div class="section" id="adapted-data-contexts">
<h1>Adapted Data Contexts<a class="headerlink" href="#adapted-data-contexts" title="Permalink to this headline">ΒΆ</a></h1>
<p>Often the data inside a context needs to be transformed in some way before it
is used:</p>
<ul class="simple">
<li>possibly in different ways by different parts on an application</li>
<li>with different transformations on different variables</li>
<li>with multiple different transformations applied sequentially</li>
</ul>
<p>And the same sequence of transformations may need to be reversed when setting
a value in to the context. These transformations may even need to be changed
depending on the situation or a user request.</p>
<p>The AdaptedDataContext class provides a framework for applying transformations
to data as it comes in and out of a context. AdaptedDataContext provides a list
of adapters in its <tt class="xref docutils literal"><span class="pre">adapters</span></tt> trait attribute, as well as <tt class="xref docutils literal"><span class="pre">push()</span></tt> and
<tt class="xref docutils literal"><span class="pre">pop()</span></tt> methods for manipulating them. On get, set, or delete operations,
the AdapterManagerMixin goes through each of the adapters and first calls the
<tt class="xref docutils literal"><span class="pre">adapt_name()</span></tt> method to perform any manipulations of the name, and then
calls <tt class="xref docutils literal"><span class="pre">adapt_getitem()</span></tt> or <tt class="xref docutils literal"><span class="pre">adapt_setitem()</span></tt> for get and set
operations respectively. Once all the adapters have had a chance to perform
transformations, the operation is applied to the underlying context.</p>
<p>To create an adapter all you need to do is to implement the IAdapter interface
by providing at least one of the <tt class="xref docutils literal"><span class="pre">adapt_name()</span></tt>, <tt class="xref docutils literal"><span class="pre">adapt_getitem()</span></tt>, or
<tt class="xref docutils literal"><span class="pre">adapt_setitem()</span></tt> methods.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">numpy</span> <span class="kn">import</span> <span class="n">ndarray</span>
<span class="kn">from</span> <span class="nn">numpy.fft</span> <span class="kn">import</span> <span class="n">fft</span><span class="p">,</span> <span class="n">ifft</span>
<span class="kn">from</span> <span class="nn">enthought.traits.api</span> <span class="kn">import</span> <span class="n">HasTraits</span>
<span class="kn">from</span> <span class="nn">enthought.contexts.api</span> <span class="kn">import</span> <span class="n">IAdapter</span>
<span class="k">class</span> <span class="nc">FFTAdapter</span><span class="p">(</span><span class="n">HasTraits</span><span class="p">):</span>
<span class="n">implements</span><span class="p">(</span><span class="n">IAdapter</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">adapt_getitem</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">context</span><span class="p">,</span> <span class="n">key</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span>
<span class="sd">"""Take Fourier transform of 1-D Numpy arrays in the context."""</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">value</span><span class="p">,</span> <span class="n">ndarray</span><span class="p">)</span> <span class="ow">and</span> <span class="nb">len</span><span class="p">(</span><span class="n">value</span><span class="o">.</span><span class="n">shape</span><span class="p">)</span> <span class="o">==</span> <span class="mf">1</span><span class="p">:</span>
<span class="k">return</span> <span class="n">key</span><span class="p">,</span> <span class="n">fft</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">adapt_setitem</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">context</span><span class="p">,</span> <span class="n">key</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span>
<span class="sd">"""Take inverse Fourier transform of 1D numpy arrays when setting into</span>
<span class="sd"> the context."""</span>
<span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">value</span><span class="p">,</span> <span class="n">ndarray</span><span class="p">)</span> <span class="ow">and</span> <span class="nb">len</span><span class="p">(</span><span class="n">value</span><span class="o">.</span><span class="n">shape</span><span class="p">)</span> <span class="o">==</span> <span class="mf">1</span><span class="p">:</span>
<span class="k">return</span> <span class="n">key</span><span class="p">,</span> <span class="n">ifft</span><span class="p">(</span><span class="n">value</span><span class="p">)</span>
</pre></div>
</div>
<p>The <tt class="xref docutils literal"><span class="pre">enthought.contexts</span></tt> package contains a number of adapters to perform
operations like masking, unit conversion, and name translation.</p>
</div>
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