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<div class="section" id="concrete-observable-properties">
<h1>Concrete Observable Properties<a class="headerlink" href="#concrete-observable-properties" title="Permalink to this headline">¶</a></h1>
<p><em>Concrete</em> OPs have values stored inside the model. They are
different from <em>Logical</em> OP whose values are calculated, or come
from outside (e.g. from a database).</p>
<p><em>Values</em> of OP are declared as class attributes in models, and OP
<em>names</em> are declared in a special class member
<tt class="docutils literal"><span class="pre">__observables__</span></tt>.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">gtkmvc</span> <span class="kn">import</span> <span class="n">Model</span>
<span class="c"># ----------------------------</span>
<span class="k">class</span> <span class="nc">MyModel</span> <span class="p">(</span><span class="n">Model</span><span class="p">):</span>
<span class="n">name</span> <span class="o">=</span> <span class="s">"Roberto"</span>
<span class="n">secondname</span> <span class="o">=</span> <span class="s">'Mario'</span>
<span class="n">surname</span> <span class="o">=</span> <span class="s">"Cavada"</span>
<span class="n">energy</span> <span class="o">=</span> <span class="mf">0.2</span> <span class="c"># needs holidays!</span>
<span class="n">status</span> <span class="o">=</span> <span class="s">"sleepy"</span>
<span class="n">__observables__</span> <span class="o">=</span> <span class="s">"name surname energy"</span><span class="o">.</span><span class="n">split</span><span class="p">()</span>
<span class="k">pass</span> <span class="c"># end of class</span>
</pre></div>
</div>
<p>In the example, <tt class="docutils literal"><span class="pre">name</span></tt>, <tt class="docutils literal"><span class="pre">surname</span></tt> and <tt class="docutils literal"><span class="pre">energy</span></tt> are all
observable, whereas <tt class="docutils literal"><span class="pre">status</span></tt> is not observable.</p>
<p>Special member <tt class="docutils literal"><span class="pre">__observables__</span></tt> is a tuple (or a list) of names
of class attributes that has to be observable. Names can contain
wildcards like <tt class="docutils literal"><span class="pre">*</span></tt> to match any sequence of characters, <tt class="docutils literal"><span class="pre">?</span></tt> to
match one single character, etc. See module <a class="reference external" href="http://docs.python.org/library/fnmatch.html">fnmatch</a> in <em>Python</em> library
for other information about possible use of wildcards in
names. Important to say that if wildcards are used, attribute names
starting with a double underscore <tt class="docutils literal"><span class="pre">__</span></tt> will be not matched.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>It is also possible (<em>but deprecated!</em>) for the user to add a
class variable called <tt class="docutils literal"><span class="pre">__properties__</span></tt>. This variable must be
a map, whose elements’ keys are names of properties, and the
associated values are the initial values. Using
<tt class="docutils literal"><span class="pre">__properties__</span></tt> is complementary to the use of
<tt class="docutils literal"><span class="pre">__observables__</span></tt>, but it is provided for backward
compatibility and should be not used in new code.
This is an example of usage of deprecated <tt class="docutils literal"><span class="pre">__properties__</span></tt>,
but you will not find another in this manual:</p>
<div class="last highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">gtkmvc</span> <span class="kn">import</span> <span class="n">Model</span>
<span class="k">class</span> <span class="nc">MyModelDeprecated</span> <span class="p">(</span><span class="n">Model</span><span class="p">):</span>
<span class="n">__properties__</span> <span class="o">=</span> <span class="p">{</span>
<span class="s">'name'</span> <span class="p">:</span> <span class="s">'Rob'</span><span class="p">,</span>
<span class="p">}</span>
<span class="k">pass</span> <span class="c"># end of class</span>
</pre></div>
</div>
</div>
<p>This is another example showing the usage of wildcards in names:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">gtkmvc</span> <span class="kn">import</span> <span class="n">Model</span>
<span class="c"># ----------------------------</span>
<span class="k">class</span> <span class="nc">MyModel</span> <span class="p">(</span><span class="n">Model</span><span class="p">):</span>
<span class="n">name</span> <span class="o">=</span> <span class="s">"Roberto"</span>
<span class="n">secondname</span> <span class="o">=</span> <span class="s">'Mario'</span>
<span class="n">surname</span> <span class="o">=</span> <span class="s">"Cavada"</span>
<span class="n">energy</span> <span class="o">=</span> <span class="mf">0.2</span> <span class="c"># needs holidays!</span>
<span class="n">entropy</span> <span class="o">=</span> <span class="mf">1.0</span>
<span class="n">enology</span> <span class="o">=</span> <span class="s">"good science"</span>
<span class="n">status</span> <span class="o">=</span> <span class="s">"sleepy"</span>
<span class="n">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"*name"</span><span class="p">,</span> <span class="s">"en????y"</span><span class="p">)</span>
<span class="k">pass</span> <span class="c"># end of class</span>
</pre></div>
</div>
<p>In the example, all attributes but <tt class="docutils literal"><span class="pre">energy</span></tt> and <tt class="docutils literal"><span class="pre">status</span></tt> are
declared to be observable.</p>
<div class="section" id="concrete-op-and-inheritance">
<h2>Concrete OP and inheritance<a class="headerlink" href="#concrete-op-and-inheritance" title="Permalink to this headline">¶</a></h2>
<p>Things so far are easy enough, but they get a bit complicated when
you derive custom models from other custom models. For example,
what happens to <em>OP</em> if you derive a new model class from the class
<tt class="docutils literal"><span class="pre">MyModel</span></tt>?</p>
<p>In this case the behavior of the <em>OP</em> trusty follows the typical Object
Oriented rules:</p>
<ul class="simple">
<li>Any concrete <em>OP</em> in base class are inherited by derived classes.</li>
<li>Derived class can override any concrete <em>OP</em> in base classes.</li>
<li>If multiple base classes defines the same <em>OP</em>, only the
first <em>OP</em> will be accessible from the derived class.</li>
</ul>
<p>For example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">gtkmvc</span> <span class="kn">import</span> <span class="n">Model</span>
<span class="k">class</span> <span class="nc">Base</span> <span class="p">(</span><span class="n">Model</span><span class="p">):</span>
<span class="n">prop1</span> <span class="o">=</span> <span class="mi">1</span>
<span class="n">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"prop1"</span><span class="p">,</span> <span class="p">)</span>
<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">Model</span><span class="o">.</span><span class="n">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span>
<span class="c"># this class is an observer of its own properties:</span>
<span class="bp">self</span><span class="o">.</span><span class="n">register_observer</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span>
<span class="k">return</span>
<span class="nd">@Model.observe</span><span class="p">(</span><span class="s">"prop1"</span><span class="p">,</span> <span class="n">assign</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">prop1_changed</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">model</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">info</span><span class="p">):</span>
<span class="k">print</span> <span class="n">model</span><span class="p">,</span> <span class="s">"prop1 changed from '</span><span class="si">%s</span><span class="s">' to '</span><span class="si">%s</span><span class="s">'"</span> <span class="o">%</span> <span class="p">(</span><span class="n">info</span><span class="o">.</span><span class="n">old</span><span class="p">,</span> <span class="n">info</span><span class="o">.</span><span class="n">new</span><span class="p">)</span>
<span class="k">return</span>
<span class="k">pass</span> <span class="c"># end of class</span>
<span class="c"># --------------------------------------------------------</span>
<span class="k">class</span> <span class="nc">Der</span> <span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="n">prop2</span> <span class="o">=</span> <span class="mi">2</span>
<span class="n">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"prop2"</span><span class="p">,)</span>
<span class="nd">@Model.observe</span><span class="p">(</span><span class="s">"prop2"</span><span class="p">,</span> <span class="n">assign</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">prop2_changed</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">model</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">info</span><span class="p">):</span>
<span class="k">print</span> <span class="bp">self</span><span class="p">,</span> <span class="s">"prop2 changed from '</span><span class="si">%s</span><span class="s">' to '</span><span class="si">%s</span><span class="s">'"</span> <span class="o">%</span> <span class="p">(</span><span class="n">info</span><span class="o">.</span><span class="n">old</span><span class="p">,</span> <span class="n">info</span><span class="o">.</span><span class="n">new</span><span class="p">)</span>
<span class="k">return</span>
<span class="k">pass</span> <span class="c"># end of class</span>
<span class="c"># --------------------------------------------------------</span>
<span class="c"># test code:</span>
<span class="n">b</span> <span class="o">=</span> <span class="n">Base</span><span class="p">()</span>
<span class="n">d</span> <span class="o">=</span> <span class="n">Der</span><span class="p">()</span>
<span class="n">d</span><span class="o">.</span><span class="n">prop2</span> <span class="o">*=</span> <span class="mi">10</span>
<span class="n">d</span><span class="o">.</span><span class="n">prop1</span> <span class="o">*=</span> <span class="mi">10</span>
<span class="n">b</span><span class="o">.</span><span class="n">prop1</span> <span class="o">*=</span> <span class="mi">10</span>
</pre></div>
</div>
<p>When executed, this script generates this output:</p>
<div class="highlight-python"><pre><__main__.Der object ...> prop2 changed from '2' to '20'
<__main__.Der object ...> prop1 changed from '1' to '10'
<__main__.Base object ...> prop1 changed from '1' to '10'</pre>
</div>
<p>Let’s analyse the example.</p>
<p>First, in the <tt class="docutils literal"><span class="pre">Base.__init__</span></tt> constructor you can see that the
instance registers itself as an observer... of itself! As we will see
in section <a class="reference internal" href="observers.html#observers"><em>Observers</em></a>, class <cite>Model</cite> derives from <cite>Observer</cite>, so
all models are also observer.</p>
<p>In the example this is exploited only to write a compact example (it
is not needed to define an additional class for the
observer). However, in complex designs it is quite common to see
models observing them self, or sub-models contained inside them.</p>
<p>Second, method <tt class="docutils literal"><span class="pre">Base.prop1_changed</span></tt> is explicitly marked to
observe property <tt class="docutils literal"><span class="pre">prop1</span></tt>.</p>
<p>Third, in class <tt class="docutils literal"><span class="pre">Der</span></tt> only the OP <tt class="docutils literal"><span class="pre">prop2</span></tt> is declared, as
<tt class="docutils literal"><span class="pre">prop1</span></tt> is inherited from class <tt class="docutils literal"><span class="pre">Base</span></tt>.
This is clearly visible in the output:</p>
<div class="highlight-python"><pre><__main__.Der object ...> prop1 changed from '1' to '10'</pre>
</div>
<p>It is possible to change type and default values of OPs in derived
class, by re-declaring the OSs. For example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Der</span> <span class="p">(</span><span class="n">Base</span><span class="p">):</span>
<span class="n">prop1</span> <span class="o">=</span> <span class="mi">3</span>
<span class="n">prop2</span> <span class="o">=</span> <span class="mi">2</span>
<span class="n">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"prop?"</span><span class="p">,)</span>
<span class="nd">@Observer.observe</span><span class="p">(</span><span class="s">"prop2"</span><span class="p">,</span> <span class="n">assign</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">prop2_changed</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">model</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">info</span><span class="p">):</span>
<span class="k">print</span> <span class="bp">self</span><span class="p">,</span> <span class="s">"prop2 changed from '</span><span class="si">%s</span><span class="s">' to '</span><span class="si">%s</span><span class="s">'"</span> <span class="o">%</span> <span class="p">(</span><span class="n">info</span><span class="o">.</span><span class="n">old</span><span class="p">,</span> <span class="n">info</span><span class="o">.</span><span class="n">new</span><span class="p">)</span>
<span class="k">return</span>
<span class="k">pass</span> <span class="c"># end of class</span>
<span class="c"># --------------------------------------------------------</span>
</pre></div>
</div>
<p>This would produce the output:</p>
<div class="highlight-python"><pre><__main__.Der object ...> prop2 changed from '2' to '20'
<__main__.Der object ...> prop1 changed from '3' to '30'
<__main__.Base object ...> prop1 changed from '1' to '10'</pre>
</div>
<p>As you can see, <tt class="docutils literal"><span class="pre">d.prop1</span></tt> overrides the <em>OP</em> <tt class="docutils literal"><span class="pre">prop1</span></tt> defined
in <tt class="docutils literal"><span class="pre">Base</span></tt> (they have different initial values now).</p>
</div>
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<li><a class="reference internal" href="#">Concrete Observable Properties</a><ul>
<li><a class="reference internal" href="#concrete-op-and-inheritance">Concrete OP and inheritance</a></li>
</ul>
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