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<div class="section" id="observable-properties">
<span id="op-top"></span><h1>Observable Properties<a class="headerlink" href="#observable-properties" title="Permalink to this headline">¶</a></h1>
<p>Observable Properties (<em>OP</em>) is a powerful mechanism which
implement the <em>Observer Pattern</em>.</p>
<p>The mechanism which allows a part of the data contained in models
to be observed by entities called <em>Observers</em>. It is fully
automatic, as its management is carried out transparently by the
base class <tt class="docutils literal"><span class="pre">Model</span></tt>.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Note:</th><td class="field-body">This section mainly focuses on OP in <em>Models</em>. The use of
<cite>Observer</cite> here is anticipated only for examples. The section
<a class="reference internal" href="observers.html#observers"><em>Observers</em></a> presents full details about them.</td>
</tr>
</tbody>
</table>
<p>Here a quick example is shown here, later all details are
presented.</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="p">,</span> <span class="n">Observer</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">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"name"</span><span class="p">,)</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">MyObserver</span> <span class="p">(</span><span class="n">Observer</span><span class="p">):</span>
<span class="nd">@Observer.observe</span><span class="p">(</span><span class="s">"name"</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">notification</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="s">"'name' changed from"</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="s">"to"</span><span class="p">,</span> <span class="n">info</span><span class="o">.</span><span class="n">new</span>
<span class="k">return</span>
<span class="k">pass</span> <span class="c"># end of class</span>
<span class="c"># ----------------------------</span>
<span class="n">m</span> <span class="o">=</span> <span class="n">MyModel</span><span class="p">()</span>
<span class="n">o</span> <span class="o">=</span> <span class="n">MyObserver</span><span class="p">(</span><span class="n">m</span><span class="p">)</span>
<span class="n">m</span><span class="o">.</span><span class="n">name</span> <span class="o">=</span> <span class="s">"Tobias"</span>
</pre></div>
</div>
<p>In models, OPs are declared explicitly, and in observers we define
methods which will be called when OPs are changed. In the example,
when <tt class="docutils literal"><span class="pre">m.name</span></tt> is changed in the last line, method
<tt class="docutils literal"><span class="pre">MyObserver.notification</span></tt> is called automatically to notify the
observer. All details about observers will be presented in section
<a class="reference internal" href="observers.html#observers"><em>Observers</em></a>, in particular about what <cite>assign=True</cite> means.</p>
<p>Controllers are also observers, so the OP pattern clicks well with
the MVC pattern.</p>
<p>If the example looks smooth and relatively easy, the topic is much
more complex. OPs can be <em>concrete</em> or <em>logical</em>, and can be values
(like in the previous example), or complex objects like containers or
user’s classes. All these differences add complexity which will be
described in details in the following sections.</p>
<div class="section" id="concrete-observable-properties">
<span id="opconc"></span><h2>Concrete Observable Properties<a class="headerlink" href="#concrete-observable-properties" title="Permalink to this headline">¶</a></h2>
<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">
<h3>Concrete OP and inheritance<a class="headerlink" href="#concrete-op-and-inheritance" title="Permalink to this headline">¶</a></h3>
<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>
</div>
<div class="section" id="logical-observable-properties">
<span id="oplog"></span><h2>Logical Observable Properties<a class="headerlink" href="#logical-observable-properties" title="Permalink to this headline">¶</a></h2>
<p><em>Logical</em> OPs are properties whose values are not necessarily
stored in the model, but which are read and written by a pair of
getter/setter methods.</p>
<p>This make logical OPs ideal for:</p>
<ul class="simple">
<li>Values calculated out of other OPs (which can be either logical
or concrete).</li>
<li>Values living outside the model, like e.g. in a database, or in a
remote server.</li>
</ul>
<p>Logical OPs are declared like concrete OPs, but no correspoding
attributes have to appear in the class. Their name have to appear
only within the special member <tt class="docutils literal"><span class="pre">__observables__</span></tt>.
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="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">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"name"</span><span class="p">,</span> <span class="s">"happiness"</span><span class="p">)</span>
<span class="k">pass</span> <span class="c"># end of class</span>
<span class="c"># ----------------------------</span>
</pre></div>
</div>
<p>In the example, <tt class="docutils literal"><span class="pre">name</span></tt> is a concrete property, whereas
<tt class="docutils literal"><span class="pre">happiness</span></tt> is a logical property, as no corresponding attribute
exists in class <tt class="docutils literal"><span class="pre">MyModel</span></tt>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>Notice that names of logical OPs occurring within the
special member <tt class="docutils literal"><span class="pre">__observables__</span></tt> cannot contain wildcards like
concrete properties.</p>
<p class="last">The reasons for this limitation is obvious, as wildcards
can be used to match only class attributes.)</p>
</div>
<p>However, a logical OP’s value is taken from a getter method, and
for a read/write OP the values are stored through a setter
method. Defining a getter is mandatory, while defining a setter is
required only for writable logical OPs.</p>
<p>getter/setter methods can be defined by exploiting decorators, or
by exploiting a naming convention.</p>
<div class="section" id="use-of-decorators-for-defining-getters-and-or-setters">
<h3>Use of decorators for defining getters and/or setters<a class="headerlink" href="#use-of-decorators-for-defining-getters-and-or-setters" title="Permalink to this headline">¶</a></h3>
<p>Decorators <tt class="docutils literal"><span class="pre">@Model.getter</span></tt> and <tt class="docutils literal"><span class="pre">@Model.setter</span></tt> can be used for
defining logical OPs getter and setter respectively. The syntax and
semantics are very similar to the python <tt class="docutils literal"><span class="pre">@property</span></tt>
decorator.</p>
<p>E.g. for logical OP <tt class="docutils literal"><span class="pre">happiness</span></tt> in the previous 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="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">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"name"</span><span class="p">,</span> <span class="s">"happiness"</span><span class="p">)</span>
<span class="n">_a_value</span> <span class="o">=</span> <span class="mf">1.0</span> <span class="c"># support for happiness</span>
<span class="nd">@Model.getter</span>
<span class="k">def</span> <span class="nf">happiness</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_a_value</span>
<span class="nd">@Model.setter</span>
<span class="k">def</span> <span class="nf">happiness</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span> <span class="bp">self</span><span class="o">.</span><span class="n">_a_value</span> <span class="o">=</span> <span class="nb">max</span><span class="p">(</span><span class="mf">1.0</span><span class="p">,</span> <span class="n">value</span><span class="p">)</span>
<span class="k">pass</span> <span class="c"># end of class</span>
<span class="c"># ----------------------------</span>
</pre></div>
</div>
<p>It is possible to define getter/setter methods which serve multiple
logical OPs.
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="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">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"name"</span><span class="p">,</span> <span class="s">"happiness"</span><span class="p">,</span> <span class="s">"energy"</span><span class="p">)</span>
<span class="n">_a_value</span> <span class="o">=</span> <span class="mf">1.0</span> <span class="c"># support for happiness</span>
<span class="nd">@Model.getter</span><span class="p">(</span><span class="s">"happiness"</span><span class="p">,</span> <span class="s">"energy"</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">a_getter_for_several_ops</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
<span class="k">if</span> <span class="s">"energy"</span> <span class="o">==</span> <span class="n">name</span><span class="p">:</span> <span class="k">return</span> <span class="mf">0.1</span> <span class="c"># constantly need holidays!</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_a_value</span>
<span class="nd">@Model.setter</span>
<span class="k">def</span> <span class="nf">happiness</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span> <span class="bp">self</span><span class="o">.</span><span class="n">_a_value</span> <span class="o">=</span> <span class="nb">max</span><span class="p">(</span><span class="mf">1.0</span><span class="p">,</span> <span class="n">value</span><span class="p">)</span>
<span class="k">pass</span> <span class="c"># end of class</span>
<span class="c"># ----------------------------</span>
</pre></div>
</div>
<p>In the example, the decorator <tt class="docutils literal"><span class="pre">@Model.getter</span></tt> is used with
arguments, which have to be the string names of all properties
which have to be handled by the decorated method. The method (the
getter in this case) will receive the name of the property along
with its other arguments.</p>
<p>Use of wildcards is allowed in decorators names, and will match all
logical OPs not exactly matched by other decorators. It is an error
condition if multiple matches are found when matching logical OPs
specified with wildcards. For example this is perfectly legal:</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">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"name"</span><span class="p">,</span> <span class="s">"energy"</span><span class="p">,</span> <span class="s">"entropy"</span><span class="p">,</span> <span class="s">"enology"</span><span class="p">)</span>
<span class="nd">@Model.getter</span>
<span class="k">def</span> <span class="nf">energy</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">return</span> <span class="mf">0.1</span> <span class="c"># constantly need holidays!</span>
<span class="nd">@Model.getter</span><span class="p">(</span><span class="s">"enology"</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">getter1</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span> <span class="k">return</span> <span class="s">"good science!"</span>
<span class="nd">@Model.getter</span><span class="p">(</span><span class="s">"en*"</span><span class="p">)</span> <span class="c"># matches only remaining 'entropy'</span>
<span class="k">def</span> <span class="nf">getter2</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
<span class="k">assert</span> <span class="s">"entropy"</span> <span class="o">==</span> <span class="n">name</span>
<span class="k">return</span> <span class="mi">0</span>
<span class="nd">@Model.setter</span><span class="p">(</span><span class="s">"*"</span><span class="p">)</span> <span class="c"># matches "energy", "entropy", "enology"</span>
<span class="k">def</span> <span class="nf">happiness</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span>
<span class="k">print</span> <span class="s">"setter for"</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">value</span>
<span class="o">...</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>However, this example is not legal:</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">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"energy"</span><span class="p">,</span> <span class="s">"entropy"</span><span class="p">,</span> <span class="s">"enology"</span><span class="p">)</span>
<span class="nd">@Model.getter</span><span class="p">(</span><span class="s">"en*"</span><span class="p">)</span> <span class="c"># matches energy, entropy, and enology</span>
<span class="k">def</span> <span class="nf">getter1</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span> <span class="o">...</span>
<span class="nd">@Model.getter</span><span class="p">(</span><span class="s">"*"</span><span class="p">)</span> <span class="c"># matches energy, entropy, and enology</span>
<span class="k">def</span> <span class="nf">getter2</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span> <span class="o">...</span>
<span class="k">pass</span> <span class="c"># end of class</span>
<span class="c"># ----------------------------</span>
</pre></div>
</div>
<p>The example does not work as ambiguity is found when resolving
wilcards.</p>
</div>
<div class="section" id="use-of-naming-convention-for-defining-getters-and-or-setters">
<h3>Use of naming convention for defining getters and/or setters<a class="headerlink" href="#use-of-naming-convention-for-defining-getters-and-or-setters" title="Permalink to this headline">¶</a></h3>
<p>In some cases, the use of decorators for defining getters/setters
can be a limitation. For example, when the model is built
dynamically, like when generating proxy classes.</p>
<p>In these and other cases, the framework supports a <em>naming
convention</em> which can be used to define implicitly getters and/or
setters for logical OPs.</p>
<p>The naming convention applies to Model’s method names which are
implicitly declared as getters or setters.</p>
<ul class="simple">
<li><cite>get_<prop_name>_value(self)</cite>: A specific getter for OP <cite><prop_name></cite>.</li>
<li><cite>set_<prop_name>_value(self, value)</cite>: A specific setter for OP <cite><prop_name></cite>.</li>
<li><cite>get__value(self, name)</cite>: A generic getter receiving the name of
the property to be get.</li>
<li><cite>set__value(self, name, value)</cite>: A generic setter receiving the name of
the property to be set.</li>
</ul>
<p>As you see getters/setters can be either <em>specific</em> or
<em>generic</em>. In the former case, the getter/setter is specific for
one OP. In the latter case, getter/setter is general and will
receive the name of the property.</p>
<p>Generic getter/setter will not be called for OPs which have
specific getter/setter defined. 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="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">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"energy"</span><span class="p">,</span> <span class="s">"entropy"</span><span class="p">,</span> <span class="s">"enology"</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">get_energy_value</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">return</span> <span class="mf">0.1</span> <span class="c"># constantly need holidays!</span>
<span class="c"># getter for entropy and enology only, as energy has a specific getter</span>
<span class="k">def</span> <span class="nf">get__value</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span> <span class="o">...</span>
<span class="c"># setter for all properties</span>
<span class="k">def</span> <span class="nf">set_value</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span> <span class="o">...</span>
<span class="k">pass</span> <span class="c"># end of class</span>
<span class="c"># ----------------------------</span>
</pre></div>
</div>
<p>The first example we presented for decorators could be rewritten
as:</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">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"name"</span><span class="p">,</span> <span class="s">"energy"</span><span class="p">,</span> <span class="s">"entropy"</span><span class="p">,</span> <span class="s">"enology"</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">get_energy_value</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">return</span> <span class="mf">0.1</span> <span class="c"># constantly need holidays!</span>
<span class="k">def</span> <span class="nf">get_enology_value</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">return</span> <span class="s">"good science!"</span>
<span class="k">def</span> <span class="nf">get__value</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">):</span>
<span class="k">assert</span> <span class="s">"entropy"</span> <span class="o">==</span> <span class="n">name</span>
<span class="k">return</span> <span class="mi">0</span>
<span class="k">def</span> <span class="nf">set__value</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">value</span><span class="p">):</span>
<span class="k">print</span> <span class="s">"setter for"</span><span class="p">,</span> <span class="n">name</span><span class="p">,</span> <span class="n">value</span>
<span class="o">...</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>Of course, since in naming conventions names <em>matters</em>, some names
in the example had to be adapted.</p>
</div>
</div>
<div class="section" id="types-of-observable-properties">
<span id="optypes"></span><h2>Types of Observable Properties<a class="headerlink" href="#types-of-observable-properties" title="Permalink to this headline">¶</a></h2>
<p>In section <a class="reference internal" href="obs.html#kobs"><em>Supported types of Observable Properties</em></a> we anticipated that there exist several types
of <em>OP*s. In the examples so far we have seen only *value</em> <em>OPs</em>,
meaning that observers will be notified of any change of <em>value</em>,
i.e. when the OPs are assigned to different values <a class="footnote-reference" href="#f-spurious" id="id1">[1]</a>.</p>
<p>What would happen if the value of
the property would be a complex object like a list, or a user-defined
class, and the object would change internally?</p>
<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">MyModel</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="p">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">]</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="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="o">...</span>
<span class="k">return</span>
<span class="k">pass</span> <span class="c"># end of class</span>
<span class="n">m</span> <span class="o">=</span> <span class="n">MyModel</span><span class="p">()</span>
<span class="n">m</span><span class="o">.</span><span class="n">prop1</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">4</span><span class="p">)</span>
<span class="n">m</span><span class="o">.</span><span class="n">prop1</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="mi">5</span>
</pre></div>
</div>
<p>Last two lines of the previous example actually change the <em>OP</em>
internally, that is different from <em>assigning</em> a new value to the
property like in <tt class="docutils literal"><span class="pre">m.prop1</span> <span class="pre">=</span> <span class="pre">[5,4,3,2]</span></tt> that would trigger an
<em>assign</em> notifications like those seen in previous examples. Similar
problem is found when the property is assigned to a class instance,
and then a method that change the instance is called.</p>
<div class="section" id="supported-objects">
<h3>Supported objects<a class="headerlink" href="#supported-objects" title="Permalink to this headline">¶</a></h3>
<p>In this section only the model-side will be presented. In the section
dedicated to observers, we will see how changes occurring to this
objects are notified.</p>
<div class="section" id="mutable-containers">
<h4>Mutable containers<a class="headerlink" href="#mutable-containers" title="Permalink to this headline">¶</a></h4>
<p>The framework <em>MVC-O</em> provides a full support for python mutable
containers like <em>lists</em> and <em>maps</em>. 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="p">,</span> <span class="n">Observer</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">myint</span> <span class="o">=</span> <span class="mi">0</span>
<span class="n">mylist</span> <span class="o">=</span> <span class="p">[]</span>
<span class="n">mymap</span> <span class="o">=</span> <span class="p">{}</span>
<span class="n">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"my*"</span><span class="p">,</span> <span class="p">)</span>
<span class="k">pass</span> <span class="c"># end of class</span>
</pre></div>
</div>
<p>This covers those cases where you have your <em>OPs</em> holding mutable
sequence values.</p>
</div>
<div class="section" id="class-instances">
<h4>Class Instances<a class="headerlink" href="#class-instances" title="Permalink to this headline">¶</a></h4>
<p>What if the value is a user-defined class instance? Suppose a class
has a method changing the content instance. The idea is that observers
are notified when the <em>method</em> is called, with the possibility to
choose if being notified <em>before</em> or <em>after</em> the call.</p>
<p>However, how can the user declare that method <tt class="docutils literal"><span class="pre">M</span></tt> <em>does changes</em> the
instance? Two mechanism are provided by the framework:</p>
<ul class="simple">
<li>For already existing classes. In this cases the declaration occurs
when the instance is assigned to the <em>OP</em> in the model.</li>
<li>For ad-hoc and new classes. In this case the method will be
<em>declared</em> as <em>Observable</em> at the class level, through a
special <em>decorator</em> provided by the framework. This is the
preferable manner.</li>
</ul>
<p>Examples for new classes:</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="p">,</span> <span class="n">Observable</span>
<span class="c"># ----------------------------------------------------------------------</span>
<span class="k">class</span> <span class="nc">AdHocClass</span> <span class="p">(</span><span class="n">Observable</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">Observable</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="bp">self</span><span class="o">.</span><span class="n">val</span> <span class="o">=</span> <span class="mi">0</span>
<span class="k">return</span>
<span class="c"># this way the method is declared as 'observed':</span>
<span class="nd">@Observable.observed</span>
<span class="k">def</span> <span class="nf">change</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="bp">self</span><span class="o">.</span><span class="n">val</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="c"># this is NOT observed (and it does not change the instance):</span>
<span class="k">def</span> <span class="nf">is_val</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">val</span><span class="p">):</span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">val</span> <span class="o">==</span> <span class="n">val</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">MyModel</span> <span class="p">(</span><span class="n">Model</span><span class="p">):</span>
<span class="n">obj</span> <span class="o">=</span> <span class="n">AdHocClass</span><span class="p">()</span>
<span class="n">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"obj"</span><span class="p">,)</span>
<span class="k">pass</span> <span class="c"># end of class</span>
</pre></div>
</div>
<p>As you can see, declaring a class as <em>observable</em> is as simple as
deriving from <tt class="docutils literal"><span class="pre">gtkmvc.Observable</span></tt> and decorating
those class methods that must be observed with the decorator
<tt class="docutils literal"><span class="pre">gtkmvc.Observable.observed</span></tt> (decorators are supported by
Python version 2.4 and later only).</p>
<p>However, sometimes we want to reuse existing classes and it is not
possible to derive them from <tt class="docutils literal"><span class="pre">gtkmvc.Observable</span></tt>. In this case
declaration of the methods to be observed can be done at time of
declaration of the corresponding <em>OP</em>. In this case the <em>value</em> to be
assigned to the <em>OP</em> must be a triple <tt class="docutils literal"><span class="pre">(class,</span> <span class="pre">instance,</span>
<span class="pre">method_names></span></tt>, where:</p>
<dl class="docutils">
<dt>class</dt>
<dd>Is the <tt class="docutils literal"><span class="pre">class</span></tt> of the object to be observed.</dd>
<dt>instance</dt>
<dd>Is the object to be observed.</dd>
<dt>method_names</dt>
<dd>Is a tuple of strings, representing the method
names of the instance to be observed.</dd>
</dl>
<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="c">#----------------------------------------------------------------------</span>
<span class="c"># This is a class the used cannot/don't want to change</span>
<span class="k">class</span> <span class="nc">HolyClass</span> <span class="p">(</span><span class="nb">object</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="bp">self</span><span class="o">.</span><span class="n">val</span> <span class="o">=</span> <span class="mi">0</span>
<span class="k">def</span> <span class="nf">change</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="bp">self</span><span class="o">.</span><span class="n">val</span> <span class="o">+=</span> <span class="mi">1</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">MyModel</span> <span class="p">(</span><span class="n">Model</span><span class="p">):</span>
<span class="n">obj</span> <span class="o">=</span> <span class="p">(</span><span class="n">HolyClass</span><span class="p">,</span> <span class="n">HolyClass</span><span class="p">(),</span> <span class="p">(</span><span class="s">'change'</span><span class="p">,))</span>
<span class="n">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"obj"</span><span class="p">,)</span>
<span class="k">pass</span> <span class="c"># end of class</span>
</pre></div>
</div>
</div>
<div class="section" id="signals">
<h4>Signals<a class="headerlink" href="#signals" title="Permalink to this headline">¶</a></h4>
<p>Finally, <em>OP</em> can hold special values that are <em>signals</em> that can be
used to notify observers that certain <em>events</em> occurred.</p>
<p>To declare an <em>OP</em> as a signal, the value of the <em>OP</em> must be an
instance of class <tt class="docutils literal"><span class="pre">gtkmvc.Signal</span></tt>. To notify an event,
the model can then invoke method <tt class="docutils literal"><span class="pre">emit</span></tt> of the <em>OP</em>. Emitting a
signal can carry an optional argument.</p>
<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="p">,</span> <span class="n">Signal</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">sgn</span> <span class="o">=</span> <span class="n">Signal</span><span class="p">()</span>
<span class="n">__observables__</span> <span class="o">=</span> <span class="p">(</span><span class="s">"sgn"</span><span class="p">,)</span>
<span class="k">pass</span>
<span class="k">if</span> <span class="n">__name__</span> <span class="o">==</span> <span class="s">"__main__"</span><span class="p">:</span>
<span class="n">m</span> <span class="o">=</span> <span class="n">MyModel</span><span class="p">()</span>
<span class="n">m</span><span class="o">.</span><span class="n">sgn</span><span class="o">.</span><span class="n">emit</span><span class="p">()</span> <span class="c"># we emit a signal</span>
<span class="n">m</span><span class="o">.</span><span class="n">sgn</span><span class="o">.</span><span class="n">emit</span><span class="p">(</span><span class="s">"hello!"</span><span class="p">)</span> <span class="c"># with argument</span>
<span class="k">pass</span>
</pre></div>
</div>
<p>In the <tt class="docutils literal"><span class="pre">examples</span></tt>, there are several examples that show how
different types of <em>OPs</em> can be used. Of course all available types
can be used in all available kind of model classes, with or without
multi-threading support.</p>
</div>
</div>
<div class="section" id="class-vs-instance-members-as-ops">
<h3>Class vs Instance members as OPs<a class="headerlink" href="#class-vs-instance-members-as-ops" title="Permalink to this headline">¶</a></h3>
<p>So far in our examples, all OPs were class members:</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">MyModel</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">10</span>
<span class="n">prop2</span> <span class="o">=</span> <span class="p">[]</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="k">pass</span> <span class="c"># end of class</span>
</pre></div>
</div>
<p>Using class vs instance attributes is not an issue when they are
assigned:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">m1</span> <span class="o">=</span> <span class="n">MyModel</span><span class="p">()</span>
<span class="n">m2</span> <span class="o">=</span> <span class="n">MyModel</span><span class="p">()</span>
<span class="n">m1</span><span class="o">.</span><span class="n">prop1</span> <span class="o">=</span> <span class="mi">5</span>
<span class="n">m2</span><span class="o">.</span><span class="n">prop1</span> <span class="o">=</span> <span class="mi">15</span>
</pre></div>
</div>
<p>In this case after the assignment <cite>m1</cite> and <cite>m2</cite> will have their own
value for attribute <cite>prop1</cite>.</p>
<p>However, when dealing with attributes whose type is a class instances,
like for example a list, you must keep in mind the attribute sharing.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">m1</span><span class="o">.</span><span class="n">prop2</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="k">print</span> <span class="n">m2</span><span class="o">.</span><span class="n">prop2</span> <span class="c"># prints [1] !</span>
</pre></div>
</div>
<p>If attribute sharing is not what you want, simply assign OPs in the
model’s constructor:</p>
<div class="highlight-python"><div class="highlight"><pre><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">prop1</span> <span class="o">=</span> <span class="mi">10</span>
<span class="n">prop2</span> <span class="o">=</span> <span class="p">[]</span> <span class="c"># may be any value actually</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="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="n">MyModel</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="bp">self</span><span class="o">.</span><span class="n">prop2</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">return</span>
<span class="k">pass</span> <span class="c"># end of class</span>
</pre></div>
</div>
<p>Now <cite>m1.prop2</cite> and <cite>m2.prop2</cite> are different objects, and sharing no
longer occurs.</p>
<p class="rubric">Section Notes</p>
<table class="docutils footnote" frame="void" id="f-spurious" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id1">[1]</a></td><td>Actually there exist <em>spurious</em> assign notifications,
which are issued also when there is no change in the
value of an OP, e.g. when an OP is assigned to
itself.</td></tr>
</tbody>
</table>
</div>
</div>
<div class="section" id="error-and-warning-conditions-with-logical-ops">
<span id="opconstr"></span><h2>Error and Warning conditions with logical OPs<a class="headerlink" href="#error-and-warning-conditions-with-logical-ops" title="Permalink to this headline">¶</a></h2>
<p>When dealing with logical OPs and in particular with getter/setter
pairs, there are complex conditions and behaviours of the framework
which may be confusing. Here those conditions are listed and
explained.</p>
<div class="section" id="error-conditions">
<h3>Error conditions<a class="headerlink" href="#error-conditions" title="Permalink to this headline">¶</a></h3>
<ul>
<li><p class="first"><strong>A logical OP has no associated getter.</strong></p>
<p>Getters are mandatory for logical OPs.</p>
</li>
<li><p class="first"><strong>OP matched by multiple getters/setters.</strong></p>
<p>Each OP must be matched exactly with one getter and optionally with
one setter. It is an error condition any multiple matching.</p>
</li>
<li><p class="first"><strong>Exactly the same pattern was used for one or more getters (setters).</strong></p>
<p>This is a specialization of previous case (multiple matching).</p>
</li>
</ul>
</div>
<div class="section" id="warning-conditions">
<h3>Warning conditions<a class="headerlink" href="#warning-conditions" title="Permalink to this headline">¶</a></h3>
<p>Warning are issued only if the devlopers enables them. In released
applications, warnings should be not visible by default, to avoid
worrying the application user.</p>
<p>When developing, it is important to enable warnings, though.</p>
<ul>
<li><p class="first"><strong>A setter has no corresponing getter.</strong></p>
<p>When a setter has no getter, the setter is simply ignored.</p>
</li>
<li><p class="first"><strong>Getter/setter defined for concrete OPs.</strong></p>
<p>When a getter and/or a setter is defined for a concrete OP (not a
<em>logical</em> OP), the getter/setter are ignored.</p>
</li>
<li><p class="first"><strong>Getter/setter defined for non-existing logical OP.</strong></p>
<p>Getters/setters whose pattern do not match any existing logical OP,
are ignored.</p>
</li>
</ul>
</div>
</div>
<div class="section" id="special-members-for-observable-properties">
<h2>Special members for Observable Properties<a class="headerlink" href="#special-members-for-observable-properties" title="Permalink to this headline">¶</a></h2>
<p>Classes derived from Model, that exports <em>OPs</em>, have several special
members. Advanced users might be interested in overriding some of them,
but in general they should be considered as private members. They are
explained here for the sake of completeness.</p>
<dl class="docutils">
<dt><tt class="docutils literal"><span class="pre">__observables__</span></tt></dt>
<dd>A class (static) member that lists property
names. This must be provided as either a tuple or a list by the
user. Wilcards in names can be used to match property names, but
properties with names starting with a double underscore
<tt class="docutils literal"><span class="pre">__</span></tt> will be not matched.</dd>
<dt><tt class="docutils literal"><span class="pre">__properties__</span></tt></dt>
<dd>(Deprecated, do not use anymore) A dictionary mapping
observable properties names and their initial value. This
variable has been substituted by __observables__.</dd>
<dt><tt class="docutils literal"><span class="pre">__derived_properties__</span></tt></dt>
<dd>(Deprecated) Automatically generated static member
that maps the <em>OPs</em> exported by all base classes. This does not
contain <em>OPs</em> that the class overrides.</dd>
<dt><tt class="docutils literal"><span class="pre">_prop_<property_name></span></tt></dt>
<dd>This is an
auto-generated variable holding the property value. For example,
a property called <tt class="docutils literal"><span class="pre">x</span></tt> will generate a variable called
<tt class="docutils literal"><span class="pre">_prop_x</span></tt>.</dd>
<dt><tt class="docutils literal"><span class="pre">get_prop_<property_name></span></tt></dt>
<dd>This public method
is the getter for the property. It is automatically generated only
if the user does not define one. This means that the user can change
the behavior of it by defining their own method. For example, for
property <tt class="docutils literal"><span class="pre">x</span></tt> the method is <tt class="docutils literal"><span class="pre">get_prop_x</span></tt>. This
method gets only self and returns the corresponding property value.</dd>
<dt><tt class="docutils literal"><span class="pre">set_prop_<property_name></span></tt></dt>
<dd>This public method
is customizable like
<tt class="docutils literal"><span class="pre">get_prop_<property_name></span></tt>. This does not return
anything, and gets self and the value to be assigned to the
property. The default auto-generated code also calls method
<tt class="docutils literal"><span class="pre">gtkmvc.Model.notify_property_change</span></tt> to notify the
change to all registered observers.</dd>
</dl>
<p>For further details about this topic see meta-classes <tt class="docutils literal"><span class="pre">PropertyMeta</span></tt>
and <tt class="docutils literal"><span class="pre">ObservablePropertyMeta</span></tt> from package <tt class="docutils literal"><span class="pre">support</span></tt>.</p>
</div>
</div>
</div>
</div>
</div>
<div class="sphinxsidebar">
<div class="sphinxsidebarwrapper">
<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Observable Properties</a><ul>
<li><a class="reference internal" href="#concrete-observable-properties">Concrete Observable Properties</a><ul>
<li><a class="reference internal" href="#concrete-op-and-inheritance">Concrete OP and inheritance</a></li>
</ul>
</li>
<li><a class="reference internal" href="#logical-observable-properties">Logical Observable Properties</a><ul>
<li><a class="reference internal" href="#use-of-decorators-for-defining-getters-and-or-setters">Use of decorators for defining getters and/or setters</a></li>
<li><a class="reference internal" href="#use-of-naming-convention-for-defining-getters-and-or-setters">Use of naming convention for defining getters and/or setters</a></li>
</ul>
</li>
<li><a class="reference internal" href="#types-of-observable-properties">Types of Observable Properties</a><ul>
<li><a class="reference internal" href="#supported-objects">Supported objects</a><ul>
<li><a class="reference internal" href="#mutable-containers">Mutable containers</a></li>
<li><a class="reference internal" href="#class-instances">Class Instances</a></li>
<li><a class="reference internal" href="#signals">Signals</a></li>
</ul>
</li>
<li><a class="reference internal" href="#class-vs-instance-members-as-ops">Class vs Instance members as OPs</a></li>
</ul>
</li>
<li><a class="reference internal" href="#error-and-warning-conditions-with-logical-ops">Error and Warning conditions with logical OPs</a><ul>
<li><a class="reference internal" href="#error-conditions">Error conditions</a></li>
<li><a class="reference internal" href="#warning-conditions">Warning conditions</a></li>
</ul>
</li>
<li><a class="reference internal" href="#special-members-for-observable-properties">Special members for Observable Properties</a></li>
</ul>
</li>
</ul>
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