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297 lines
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<div class="section" id="instrospection">
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<h1>Instrospection<a class="headerlink" href="#instrospection" title="Permalink to this headline">¶</a></h1>
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<p>Python’s introspection capabilites. First, we shall use the prompt.</p>
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<div class="section" id="the-prompt">
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<h2>The prompt<a class="headerlink" href="#the-prompt" title="Permalink to this headline">¶</a></h2>
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<p>Type <cite>python3</cite> in the prompt. It gives you a prompt, which is the python prompt:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="go">>>></span>
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</pre></div>
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</div>
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<p>The prompt enables us to deeply analyse the fundamentals of the language.
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It is interesting for a good understanding of the concepts.</p>
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<p>For example, <strong>introspection</strong>. Introspection means finding informations
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about each element you want to manipulate:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">locals</span><span class="p">()</span>
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<span class="go">{'__name__': '__main__', '__package__': None, '__doc__': None,</span>
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<span class="go">'__builtins__': <module 'builtins' (built-in)>, (...) }</span>
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<span class="go">>>></span>
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</pre></div>
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</div>
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<dl class="glossary docutils">
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<dt id="term-locals">locals</dt>
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<dd>The <cite>locals()</cite> builtin function lists the variables that lives in the
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current namespace.</dd>
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<dt id="term-globals">globals</dt>
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<dd>The <cite>globals()</cite> builtin function lists the variables that lives in the
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general namespace.</dd>
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</dl>
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<p><cite>locals()</cite> in the global namespace and <cite>locals()`</cite> in a local namespace
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(a function’s namespace):</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">myfunc</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
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<span class="gp">... </span> <span class="n">a</span> <span class="o">=</span> <span class="mi">2</span>
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<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="nb">locals</span><span class="p">())</span>
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<span class="gp">...</span>
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<span class="gp">>>> </span><span class="nb">locals</span><span class="p">()</span>
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<span class="go">{'__package__': None, '__spec__': None, (...)'__name__': '__main__', '__builtins__': <module 'builtins' (built-in)>}</span>
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<span class="gp">>>> </span><span class="c1"># we can see that there's no "a" variable</span>
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<span class="gp">>>> </span><span class="n">myfunc</span><span class="p">(</span><span class="s2">"toto"</span><span class="p">)</span>
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<span class="go">{'x': 'toto', 'a': 2}</span>
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<span class="gp">>>> </span><span class="c1"># in the function there is a "a" variable</span>
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</pre></div>
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</div>
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<p>When we open a prompt, the general namespace and the local namespace are the same.</p>
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<dl class="glossary docutils">
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<dt id="term-builtins">builtins</dt>
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<dd>The <cite>__builtins__`</cite> module is a special module :
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it is the only namespace which is automaticaly imported.
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It means that the variables function that are in the builtins are always
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accessible. You can always call them.</dd>
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</dl>
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<p>For example, you can use the function <cite>dir</cite> which is directly accessible
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without importing any module:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">dir</span><span class="p">()</span>
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<span class="go">['__builtins__', '__cached__', '__doc__', '__loader__', '__name__', ...]</span>
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<span class="go">>>></span>
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</pre></div>
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</div>
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<p>In fact, the <cite>dir()</cite> function lives in the <cite>__builtins__</cite>:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">__builtins__</span><span class="o">.</span><span class="n">dir</span><span class="p">()</span>
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<span class="go">['__builtins__', '__cached__', '__doc__', '__loader__', '__name__', ...]</span>
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</pre></div>
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</div>
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<p>type:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">help</span><span class="p">(</span><span class="nb">dir</span><span class="p">)</span>
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</pre></div>
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</div>
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<p>to have help on a given function or module.</p>
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<p><cite>__doc__</cite>: this namespace’s docstring
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<cite>__package__</cite>: the current namespace</p>
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<p><cite>__name__</cite> is the name of the current namespace, which is <cite>__main__</cite>:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="vm">__name__</span>
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<span class="go">'__main__'</span>
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<span class="go">>>></span>
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</pre></div>
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</div>
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<p>why is it <cite>__main__</cite> ? Because we are located in the global namespace.</p>
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</div>
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<div class="section" id="modules">
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<h2>Modules<a class="headerlink" href="#modules" title="Permalink to this headline">¶</a></h2>
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<p>A module is a namespace, it is a pyhton file that you can import in another module.
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A python file is intended to become a library, but you can use it as a script.</p>
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<p>If you want to use module as a script, the good pratice is to fix its behavior with:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__main__'</span><span class="p">:</span>
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<span class="n">do_this</span><span class="p">()</span>
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</pre></div>
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</div>
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<p>It means that if you launch the module in the global namespace, then the module
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is not used as a library but as a standalone script.
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The good practice in a module is to do nothing.
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If you launch:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">do_this</span><span class="p">()</span>
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</pre></div>
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</div>
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<p>without the test condition:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">'__main__'</span><span class="p">:</span>
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</pre></div>
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</div>
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<p>when you import the module:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">mymodule</span>
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</pre></div>
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</div>
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<p>it will launch the <cite>do_this</cite> function, wich is not a intended behavior for a library.
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A library is just a set of function/classes that are available in a given namespace.
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A script is intended to do something when launched, not a library.</p>
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<p>What are scripts ?
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Scripts are executable file, they have a she bang:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="ch">#!/usr/bin/env python3</span>
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</pre></div>
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</div>
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<p>You can import some other libraries in your script, and it becomes an application:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">my_second_module</span>
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</pre></div>
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</div>
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<p>or:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">my_second_module</span> <span class="k">import</span> <span class="n">my_function</span>
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</pre></div>
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</div>
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<p>or:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">my_second_module</span> <span class="k">import</span> <span class="n">my_function</span> <span class="k">as</span> <span class="n">my_function_alias</span>
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</pre></div>
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</div>
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<p>or:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">my_second_module</span> <span class="k">as</span> <span class="nn">my_second_module_alias</span>
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</pre></div>
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</div>
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</div>
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<div class="section" id="assinging-a-variable">
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<h2>Assinging a variable<a class="headerlink" href="#assinging-a-variable" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">a</span> <span class="o">=</span> <span class="mf">42.</span>
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<span class="gp">>>> </span><span class="nb">type</span><span class="p">(</span><span class="n">a</span><span class="p">)</span>
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<span class="go"><class 'float'></span>
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</pre></div>
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</div>
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<p>what is dynamic typing ? You can set some other value to the <cite>a</cite> variable that
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has nothing to do with the previous type:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">a</span> <span class="o">=</span> <span class="mi">42</span><span class="n">j</span>
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<span class="gp">>>> </span><span class="nb">type</span><span class="p">(</span><span class="n">a</span><span class="p">)</span>
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<span class="go"><class 'complex'></span>
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<span class="go">>>></span>
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</pre></div>
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</div>
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</div>
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<div class="section" id="functions">
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<h2>Functions<a class="headerlink" href="#functions" title="Permalink to this headline">¶</a></h2>
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<p>This function:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">my_function</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">):</span>
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<span class="gp">... </span> <span class="sd">"""this is my func docstring"""</span>
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<span class="gp">...</span>
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</pre></div>
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</div>
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<p>is equivalent to:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">my_function</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">):</span>
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<span class="gp">... </span> <span class="sd">"""this is my func docstring"""</span>
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<span class="gp">... </span> <span class="k">return</span> <span class="kc">None</span>
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</pre></div>
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</div>
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<p>There are no procedures in python (a procedure returns nothing). It means that
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a function return always someting. Even if you don’t <em>return</em> something: it
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returns <cite>None</cite>, which is something:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">result</span> <span class="o">=</span> <span class="n">my_function</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>
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<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
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<span class="go">None</span>
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<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">my_function</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">))</span>
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<span class="go">None</span>
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</pre></div>
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</div>
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<p><strong>In python, a function is… an object</strong>. Yes. What is a docstring’s function
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? A Docstring is the <cite>__doc__</cite> attribute of the <cite>my_function</cite> object:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">my_function</span><span class="o">.</span><span class="vm">__doc__</span>
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<span class="go">'this is my func docstring'</span>
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<span class="go">>>></span>
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</pre></div>
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</div>
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<p>In python, absolutely everything is an object… even the functions:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">type</span> <span class="p">(</span><span class="n">my_function</span><span class="p">)</span>
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<span class="go"><class 'function'></span>
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<span class="go">>>></span>
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</pre></div>
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</div>
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<p>A function is an instance of the <cite>function</cite> class.</p>
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<p>Unnamed arguments in a function:</p>
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|
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">my_fonction</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">,</span> <span class="o">**</span><span class="n">kwargs</span><span class="p">):</span>
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<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"arguments : "</span><span class="p">,</span> <span class="nb">str</span><span class="p">(</span><span class="n">args</span><span class="p">))</span>
|
|||
|
|
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"named argumments : "</span><span class="p">,</span> <span class="nb">str</span><span class="p">(</span><span class="n">kwargs</span><span class="p">))</span>
|
|||
|
|
<span class="gp">...</span>
|
|||
|
|
<span class="gp">>>> </span><span class="n">my_fonction</span><span class="p">(</span><span class="s2">"toto"</span><span class="p">,</span> <span class="s2">"titi"</span><span class="p">,</span> <span class="n">tutu</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">tata</span><span class="o">=</span><span class="mi">3</span><span class="p">)</span>
|
|||
|
|
<span class="go">arguments : ('toto', 'titi')</span>
|
|||
|
|
<span class="go">named argumments : {'tata': 3, 'tutu': 2}</span>
|
|||
|
|
<span class="go">>>></span>
|
|||
|
|
</pre></div>
|
|||
|
|
</div>
|
|||
|
|
<div class="section" id="the-samourai-rule">
|
|||
|
|
<h3>The <em>samouraï</em> rule<a class="headerlink" href="#the-samourai-rule" title="Permalink to this headline">¶</a></h3>
|
|||
|
|
<p>A function shall return the expected result, or… kill itself
|
|||
|
|
(that is, raise and exception).</p>
|
|||
|
|
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">function_raise</span><span class="p">(</span><span class="n">x</span><span class="p">):</span>
|
|||
|
|
<span class="gp">... </span> <span class="k">if</span> <span class="ow">not</span> <span class="nb">type</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="o">==</span> <span class="nb">int</span><span class="p">:</span>
|
|||
|
|
<span class="gp">... </span> <span class="k">raise</span> <span class="ne">TypeError</span><span class="p">(</span><span class="s2">"Not the right type"</span><span class="p">)</span>
|
|||
|
|
<span class="gp">... </span> <span class="k">else</span><span class="p">:</span>
|
|||
|
|
<span class="gp">... </span> <span class="k">return</span> <span class="n">x</span> <span class="o">+</span> <span class="mi">1</span>
|
|||
|
|
<span class="gp">...</span>
|
|||
|
|
<span class="gp">>>> </span><span class="k">try</span><span class="p">:</span>
|
|||
|
|
<span class="gp">... </span> <span class="n">e</span> <span class="o">=</span> <span class="n">function_raise</span><span class="p">(</span><span class="s2">"une string"</span><span class="p">)</span>
|
|||
|
|
<span class="gp">... </span><span class="k">except</span> <span class="ne">TypeError</span><span class="p">,</span> <span class="n">e</span><span class="p">:</span>
|
|||
|
|
<span class="gp">... </span> <span class="nb">print</span> <span class="n">e</span>
|
|||
|
|
<span class="gp">...</span>
|
|||
|
|
<span class="go">Not the right type</span>
|
|||
|
|
<span class="go">>></span>
|
|||
|
|
</pre></div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
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</div>
|
|||
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|
|||
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|
|||
|
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</div>
|
|||
|
|
</div>
|
|||
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