201 lines
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201 lines
11 KiB
HTML
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<title>Kapitel 05: Komposition und Playlists</title>
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<a href="../index.html">🏠 Zur Kursübersicht</a>
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<span>›</span>
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<a href="../04_str_und_darstellung/index.html">Kapitel 04</a>
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<span>›</span>
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<span style="color: white; font-weight: 600;">Kapitel 05</span>
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<div class="header-badge">Kapitel 05</div>
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<h1>Komposition: Objekte kombinieren & filtern 🎵</h1>
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<p>Baue einen eigenen Spotify-Playlist-Manager und lerne, wie Objekte andere Objekte suchen, berechnen und filtern.</p>
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</div>
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</header>
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<main class="container">
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<!-- 1. Was ist Komposition -->
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<section class="card">
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<h2>1. Was ist Komposition?</h2>
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<p>
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In großen Anwendungen (wie Spotify, Netflix oder Schulsoftware) arbeiten viele Klassen zusammen. Wenn eine Klasse Objekte einer anderen Klasse als Attribute speichert, nennt man das <strong>Komposition</strong> (oder *"hat-ein"-Beziehung*):
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</p>
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<ul style="margin-left: 20px; margin-bottom: 15px;">
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<li>Eine <strong>Schulklasse</strong> <em>hat</em> viele <strong>Schüler</strong>.</li>
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<li>Eine <strong>Playlist</strong> <em>hat</em> viele <strong>Songs</strong>.</li>
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<li>Ein <strong>Kino</strong> <em>hat</em> viele <strong>Säle</strong>.</li>
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</ul>
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</section>
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<!-- 2. Vollständiges Beispiel: Notenmanager -->
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<section class="card">
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<h2>2. 🎒 Vollständiges Beispiel: Schüler & Schulklasse Notenmanager</h2>
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<p>Hier siehst du ein vollständiges Beispiel aus dem Schulalltag: Die Klasse <code>Schueler</code> speichert Name und Note. Die Klasse <code>Schulklasse</code> verwaltet alle Schüler, berechnet den Notendurchschnitt und sucht die Klassenbesten:</p>
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<div class="code-container">
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<div class="code-header">
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<div class="code-dots">
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<span class="code-dot dot-red"></span>
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<span class="code-dot dot-yellow"></span>
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<span class="code-dot dot-green"></span>
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</div>
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<span>Python (Komplettes Beispiel: schulklasse.py)</span>
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</div>
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<pre><span class="cm"># ==============================================================================</span>
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<span class="cm"># KLASSE 1: Ein einzelner Schüler</span>
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<span class="cm"># ==============================================================================</span>
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<span class="kw">class</span> <span class="fn">Schueler</span>:
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<span class="kw">def</span> <span class="fn">__init__</span>(<span class="var">self</span>, <span class="var">name</span>, <span class="var">note</span>):
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<span class="var">self</span>.<span class="attr">name</span> = <span class="var">name</span>
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<span class="var">self</span>.<span class="attr">note</span> = <span class="fn">float</span>(<span class="var">note</span>)
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<span class="kw">def</span> <span class="fn">__str__</span>(<span class="var">self</span>):
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<span class="kw">return</span> <span class="str">f"{self.name} (Note: {self.note:.1f})"</span>
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<span class="cm"># ==============================================================================</span>
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<span class="cm"># KLASSE 2: Die Schulklasse verwaltet viele Schüler-Objekte</span>
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<span class="cm"># ==============================================================================</span>
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<span class="kw">class</span> <span class="fn">Schulklasse</span>:
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<span class="kw">def</span> <span class="fn">__init__</span>(<span class="var">self</span>, <span class="var">klassen_name</span>):
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<span class="var">self</span>.<span class="attr">klassen_name</span> = <span class="var">klassen_name</span>
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<span class="var">self</span>.<span class="attr">schueler_liste</span> = []
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<span class="kw">def</span> <span class="fn">hinzufuegen</span>(<span class="var">self</span>, <span class="var">schueler</span>):
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<span class="var">self</span>.<span class="attr">schueler_liste</span>.<span class="fn">append</span>(<span class="var">schueler</span>)
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<span class="kw">def</span> <span class="fn">notendurchschnitt</span>(<span class="var">self</span>):
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<span class="kw">if</span> <span class="kw">not</span> <span class="var">self</span>.<span class="attr">schueler_liste</span>:
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<span class="kw">return</span> <span class="num">0.0</span>
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<span class="var">summe</span> = <span class="fn">sum</span>(<span class="var">s</span>.<span class="attr">note</span> <span class="kw">for</span> <span class="var">s</span> <span class="kw">in</span> <span class="var">self</span>.<span class="attr">schueler_liste</span>)
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<span class="kw">return</span> <span class="var">summe</span> / <span class="fn">len</span>(<span class="var">self</span>.<span class="attr">schueler_liste</span>)
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<span class="kw">def</span> <span class="fn">beste_schueler</span>(<span class="var">self</span>):
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<span class="cm"># Findet alle Schüler mit einer 1 (Note <= 1.5)</span>
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<span class="kw">return</span> [<span class="var">s</span> <span class="kw">for</span> <span class="var">s</span> <span class="kw">in</span> <span class="var">self</span>.<span class="attr">schueler_liste</span> <span class="kw">if</span> <span class="var">s</span>.<span class="attr">note</span> <= <span class="num">1.5</span>]
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<span class="cm"># Ausprobieren:</span>
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<span class="kw">if</span> <span class="var">__name__</span> == <span class="str">"__main__"</span>:
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<span class="var">klasse_9a</span> = <span class="fn">Schulklasse</span>(<span class="str">"Klasse 9a"</span>)
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<span class="var">s1</span> = <span class="fn">Schueler</span>(<span class="str">"Emma"</span>, <span class="num">1.0</span>)
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<span class="var">s2</span> = <span class="fn">Schueler</span>(<span class="str">"Lukas"</span>, <span class="num">2.3</span>)
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<span class="var">s3</span> = <span class="fn">Schueler</span>(<span class="str">"Mia"</span>, <span class="num">1.3</span>)
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<span class="var">klasse_9a</span>.<span class="fn">hinzufuegen</span>(<span class="var">s1</span>)
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<span class="var">klasse_9a</span>.<span class="fn">hinzufuegen</span>(<span class="var">s2</span>)
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<span class="var">klasse_9a</span>.<span class="fn">hinzufuegen</span>(<span class="var">s3</span>)
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<span class="fn">print</span>(<span class="str">f"Durchschnitt: {klasse_9a.notendurchschnitt():.2f}"</span>) <span class="cm"># 1.53</span>
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<span class="fn">print</span>(<span class="str">"\nBeste Schüler:"</span>)
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<span class="kw">for</span> <span class="var">einserschueler</span> <span class="kw">in</span> <span class="var">klasse_9a</span>.<span class="fn">beste_schueler</span>():
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<span class="fn">print</span>(<span class="str">f"- {einserschueler}"</span>)</pre>
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</div>
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</section>
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<!-- 3. Nützliche Kniffe -->
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<section class="card">
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<h2>3. Nützliche Kniffe für die Song-Aufgabe</h2>
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<h3>⏱️ Sekunden in "MM:SS" umrechnen</h3>
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<div class="code-container">
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<pre><span class="var">minuten</span> = <span class="var">self</span>.<span class="attr">dauer_sekunden</span> // <span class="num">60</span>
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<span class="var">sekunden</span> = <span class="var">self</span>.<span class="attr">dauer_sekunden</span> % <span class="num">60</span>
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<span class="kw">return</span> <span class="str">f"{minuten:02d}:{sekunden:02d}"</span> <span class="cm"># z.B. "03:35"</span></pre>
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</div>
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<h3>🔍 Groß- und Kleinschreibung beim Suchen ignorieren</h3>
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<div class="code-container">
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<pre><span class="kw">if</span> <span class="var">song</span>.<span class="attr">kuenstler</span>.<span class="fn">lower</span>() == <span class="var">kuenstler</span>.<span class="fn">lower</span>():
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<span class="var">treffer</span>.<span class="fn">append</span>(<span class="var">song</span>)</pre>
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</div>
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</section>
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<!-- 4. Aufgaben Card -->
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<section class="card">
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<h2>4. 🎯 Deine Aufgaben in <code>aufgabe.py</code></h2>
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<ul class="task-list">
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<li class="task-item">
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<input type="checkbox" class="task-checkbox" id="t5_1">
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<label for="t5_1" class="task-label">
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<strong>Klasse Song:</strong> <code>__init__(titel, kuenstler, dauer_sekunden)</code>, <code>formatierte_dauer()</code> ("MM:SS") und <code>__str__()</code>.
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</label>
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</li>
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<li class="task-item">
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<input type="checkbox" class="task-checkbox" id="t5_2">
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<label for="t5_2" class="task-label">
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<strong>Klasse Playlist:</strong> <code>__init__(name)</code> mit <code>self.songs = []</code>.
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</label>
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</li>
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<li class="task-item">
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<input type="checkbox" class="task-checkbox" id="t5_3">
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<label for="t5_3" class="task-label">
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<strong>Playlist Methoden:</strong> <code>song_hinzufuegen</code>, <code>anzahl_songs</code>, <code>gesamtdauer_sekunden</code>.
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</label>
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</li>
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<li class="task-item">
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<input type="checkbox" class="task-checkbox" id="t5_4">
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<label for="t5_4" class="task-label">
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<strong>Playlist Suchen:</strong> <code>finde_songs_von(kuenstler)</code> und <code>laengster_song()</code>.
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</label>
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</li>
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</ul>
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<h3>💡 Lösungshinweise (Aufklappen bei Bedarf)</h3>
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<details>
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<summary>🔍 Tipp zum längsten Song finden</summary>
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<div class="details-content">
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<div class="code-container">
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<pre><span class="kw">def</span> <span class="fn">laengster_song</span>(<span class="var">self</span>):
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<span class="kw">if</span> <span class="kw">not</span> <span class="var">self</span>.<span class="attr">songs</span>:
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<span class="kw">return</span> <span class="kw">None</span>
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<span class="var">bester_song</span> = <span class="var">self</span>.<span class="attr">songs</span>[<span class="num">0</span>]
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<span class="kw">for</span> <span class="var">s</span> <span class="kw">in</span> <span class="var">self</span>.<span class="attr">songs</span>:
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<span class="kw">if</span> <span class="var">s</span>.<span class="attr">dauer_sekunden</span> > <span class="var">bester_song</span>.<span class="attr">dauer_sekunden</span>:
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<span class="var">bester_song</span> = <span class="var">s</span>
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<span class="kw">return</span> <span class="var">bester_song</span></pre>
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</div>
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</div>
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</details>
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</section>
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<!-- 5. Testen & Navigation -->
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<section class="card">
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<h2>5. 🧪 Lösung überprüfen</h2>
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<p>Führe im Terminal im Ordner <code>05_objekte_kombinieren</code> folgenden Befehl aus:</p>
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<div class="code-container">
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<div class="code-header">
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<span>Terminal</span>
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</div>
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<pre><code>python3 test_aufgabe.py</code></pre>
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