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<div class="body" role="main">
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<section id="kicking-things-off">
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<section id="makegames-3">
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<span id="id1"></span><h2>3. Kicking things off<a class="headerlink" href="#makegames-3" title="Permalink to this headline">¶</a></h2>
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<p>The first sections of code are relatively simple, and, once written, can usually be reused in every game you consequently make. They
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will do all of the boring, generic tasks like loading modules, loading images, opening networking connections, playing music, and so
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on. They will also include some simple but effective error handling, and any customisation you wish to provide on top of functions
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provided by modules like <code class="docutils literal notranslate"><span class="pre">sys</span></code> and <code class="docutils literal notranslate"><span class="pre">pygame</span></code>.</p>
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<section id="the-first-lines-and-loading-modules">
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<span id="makegames-3-1"></span><h3>3.1. The first lines, and loading modules<a class="headerlink" href="#the-first-lines-and-loading-modules" title="Permalink to this headline">¶</a></h3>
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<p>First off, you need to start off your game and load up your modules. It's always a good idea to set a few things straight at the top of
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the main source file, such as the name of the file, what it contains, the license it is under, and any other helpful info you might
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want to give those who will be looking at it. Then you can load modules, with some error checking so that Python doesn't print out
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a nasty traceback, which non-programmers won't understand. The code is fairly simple, so I won't bother explaining any of it:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="ch">#!/usr/bin/env python</span>
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<span class="c1">#</span>
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<span class="c1"># Tom's Pong</span>
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<span class="c1"># A simple pong game with realistic physics and AI</span>
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<span class="c1"># http://tomchance.org.uk/projects/pong</span>
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<span class="c1">#</span>
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<span class="c1"># Released under the GNU General Public License</span>
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<span class="n">VERSION</span> <span class="o">=</span> <span class="s2">"0.4"</span>
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<span class="k">try</span><span class="p">:</span>
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<span class="kn">import</span> <span class="nn">sys</span>
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<span class="kn">import</span> <span class="nn">random</span>
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<span class="kn">import</span> <span class="nn">math</span>
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<span class="kn">import</span> <span class="nn">os</span>
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<span class="kn">import</span> <span class="nn">getopt</span>
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<span class="kn">import</span> <span class="nn">pygame</span>
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<span class="kn">from</span> <span class="nn">socket</span> <span class="kn">import</span> <span class="o">*</span>
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<span class="kn">from</span> <span class="nn">pygame.locals</span> <span class="kn">import</span> <span class="o">*</span>
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<span class="k">except</span> <span class="ne">ImportError</span><span class="p">,</span> <span class="n">err</span><span class="p">:</span>
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<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"couldn't load module. </span><span class="si">{</span><span class="n">err</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
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<span class="n">sys</span><span class="o">.</span><span class="n">exit</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
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</pre></div>
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</div>
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</section>
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<section id="resource-handling-functions">
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<span id="makegames-3-2"></span><h3>3.2. Resource handling functions<a class="headerlink" href="#resource-handling-functions" title="Permalink to this headline">¶</a></h3>
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<p>In the <a class="reference internal" href="ChimpLineByLine.html"><span class="doc">Line By Line Chimp</span></a> example, the first code to be written was for loading images and sounds. As these
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were totally independent of any game logic or game objects, they were written as separate functions, and were written first so
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that later code could make use of them. I generally put all my code of this nature first, in their own, classless functions; these
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will, generally speaking, be resource handling functions. You can of course create classes for these, so that you can group them
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together, and maybe have an object with which you can control all of your resources. As with any good programming environment, it's up
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to you to develop your own best practice and style.</p>
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<p>It's always a good idea to write your own resource handling functions,
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because although Pygame has methods for opening images and sounds, and other modules will have their methods of opening other
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resources, those methods can take up more than one line, they can require consistent modification by yourself, and they often don't
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provide satisfactory error handling. Writing resource handling functions gives you sophisticated, reusable code, and gives you more
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control over your resources. Take this example of an image loading function:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">load_png</span><span class="p">(</span><span class="n">name</span><span class="p">):</span>
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<span class="w"> </span><span class="sd">""" Load image and return image object"""</span>
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<span class="n">fullname</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="s2">"data"</span><span class="p">,</span> <span class="n">name</span><span class="p">)</span>
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<span class="k">try</span><span class="p">:</span>
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<span class="n">image</span> <span class="o">=</span> <span class="n">pygame</span><span class="o">.</span><span class="n">image</span><span class="o">.</span><span class="n">load</span><span class="p">(</span><span class="n">fullname</span><span class="p">)</span>
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<span class="k">if</span> <span class="n">image</span><span class="o">.</span><span class="n">get_alpha</span><span class="p">()</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
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<span class="n">image</span> <span class="o">=</span> <span class="n">image</span><span class="o">.</span><span class="n">convert</span><span class="p">()</span>
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<span class="k">else</span><span class="p">:</span>
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<span class="n">image</span> <span class="o">=</span> <span class="n">image</span><span class="o">.</span><span class="n">convert_alpha</span><span class="p">()</span>
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<span class="k">except</span> <span class="ne">FileNotFoundError</span><span class="p">:</span>
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<span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"Cannot load image: </span><span class="si">{</span><span class="n">fullname</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
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<span class="k">raise</span> <span class="ne">SystemExit</span>
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<span class="k">return</span> <span class="n">image</span><span class="p">,</span> <span class="n">image</span><span class="o">.</span><span class="n">get_rect</span><span class="p">()</span>
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</pre></div>
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</div>
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<p>Here we make a more sophisticated image loading function than the one provided by <a class="tooltip reference internal" href="../ref/image.html#pygame.image.load" title=""><code class="xref py py-func docutils literal notranslate"><span class="pre">pygame.image.load()</span></code><span class="tooltip-content">load new image from a file (or file-like object)</span></a>. Note that
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the first line of the function is a documentation string describing what the function does, and what object(s) it returns. The
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function assumes that all of your images are in a directory called data, and so it takes the filename and creates the full pathname,
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for example <code class="docutils literal notranslate"><span class="pre">data/ball.png</span></code>, using the <em class="citetitle">os</em> module to ensure cross-platform compatibility. Then it
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tries to load the image, and convert any alpha regions so you can achieve transparency, and it returns a more human-readable error
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if there's a problem. Finally it returns the image object, and its <a class="reference internal" href="../ref/rect.html#pygame.Rect" title="pygame.Rect"><code class="xref py py-class docutils literal notranslate"><span class="pre">rect</span></code></a>.</p>
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<p>You can make similar functions for loading any other resources, such as loading sounds. You can also make resource handling classes,
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to give you more flexibility with more complex resources. For example, you could make a music class, with an <code class="docutils literal notranslate"><span class="pre">__init__</span></code>
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function that loads the sound (perhaps borrowing from a <code class="docutils literal notranslate"><span class="pre">load_sound()</span></code> function), a function to pause the music, and a
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function to restart. Another handy resource handling class is for network connections. Functions to open sockets, pass data with
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suitable security and error checking, close sockets, finger addresses, and other network tasks, can make writing a game with network
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capabilities relatively painless.</p>
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<p>Remember the chief task of these functions/classes is to ensure that by the time you get around to writing game object classes,
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and the main loop, there's almost nothing left to do. Class inheritance can make these basic classes especially handy. Don't go
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overboard though; functions which will only be used by one class should be written as part of that class, not as a global
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function.</p>
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</section>
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</section>
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</section>
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<br /><br />
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<hr />
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<a href="https://github.com/pygame/pygame/edit/main/docs/reST/tut\tom_games3.rst" rel="nofollow">Edit on GitHub</a>
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<li class="nav-item nav-item-this"><a href="">Kicking things off</a></li>
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