Python: Polymorphism

Python: Polymorphism

• 1.
  Polymorphism Damian Gordon
• 2.
  Polymorphism • Polymorphism simplymeans that we can call the same method name with parameters, and depending on the parameters, it will do different things. For example: >>> print(6 * 5) >>> print(“Hello” * 5)
• 3.
  Polymorphism • Polymorphism simplymeans that we can call the same method name with parameters, and depending on the parameters, it will do different things. For example: >>> print(6 * 5) >>> print(“Hello” * 5) Mult (6, 5) Mult (“Hello”, 5)
• 4.
  Polymorphism • Polymorphism simplymeans that we can call the same method name with parameters, and depending on the parameters, it will do different things. For example: >>> print(6 * 5) >>> print(“Hello” * 5) Mult (6, 5) Mult (“Hello”, 5) 30 HelloHelloHelloHelloHello
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  Polymorphism • A morecomplicated example to consider would be to think about creating a method called play() to play an audio file. • A media player will be needed to load the AudioFile object. • The instruction to play the file might be as simple as: >>> audio_file.play( )
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  Polymorphism • However, differentaudio files use different compression algorithms (e.g. .mp3, .wma, .ogg), and some aren’t stored as compressed at all (e.g. .wav). • We can use inheritance with polymorphism to simplify the design. Each filetype is represented as a different subclass of AudioFile, and each of those has a play( ) method.
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  Polymorphism AudioFile _ _init_ _() MP3File play( ) WAVFile play( ) OGGFile play( )
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  Polymorphism class AudioFile: def __init_ _(self, filename): if not filename.endswith(self.ext): # THEN raise Exception(“Invalid format”) # ENDIF; self.filename = filename # END init() # END CLASS.
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  Polymorphism class AudioFile: def __init_ _(self, filename): if not filename.endswith(self.ext): # THEN raise Exception(“Invalid format”) # ENDIF; self.filename = filename # END init() # END CLASS. Check if the file extension of the audio being played is a known extension, self.ext is set in each of the subclasses. Raise an exception if it’s an unknown file extension If it’s a known file extension, then assign the filename passed in to self.filename
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  Polymorphism class MP3File(AudioFile): ext =“mp3” def play(self): print(“playing {} as mp3”.format(self.filename)) # END play # END CLASS.
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  Polymorphism class WAVFile(AudioFile): ext =“wav” def play(self): print(“playing {} as wav”.format(self.filename)) # END play # END CLASS.
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  Polymorphism class OGGFile(AudioFile): ext =“ogg” def play(self): print(“playing {} as ogg”.format(self.filename)) # END play # END CLASS.
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  Polymorphism • Here’s howwe run it: >>> mp3 = MP3File(“myfile.mp3”) >>> mp3.play() playing myfile.mp3 as mp3
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  Polymorphism • Here’s anotherone: >>> wav = WAVFile(“myfile.wav”) >>> wav.play() playing myfile.wav as wav
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  Polymorphism • Here’s anerror: >>> ogg_declared_as_mp3 = MP3File("myfile.ogg") Traceback (most recent call last): File "<stdin>", line 1, in <module> File "polymorphic_audio.py", line 4, in __init__ raise Exception("Invalid format") Exception: Invalid format
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  etc.