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Python3/en: multiple inheritance (#2217)
* Add __name__ check to make testing easier * Update say to call print. Add more usage examples * Move Modules section before Classes Makes more sense for when explaining inheritance * Add multiple inheritance example * Add examples for multiple inheritance * Add instance check examples * Fix multiple inheritance example * Add note on the __name__ variable
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Alexandre Constantino
ven
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@ -601,95 +601,9 @@ list(filter(lambda x: x > 5, [3, 4, 5, 6, 7])) # => [6, 7]
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[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
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[x for x in [3, 4, 5, 6, 7] if x > 5] # => [6, 7]
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####################################################
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## 5. Classes
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####################################################
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# We use the "class" operator to get a class
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class Human:
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# A class attribute. It is shared by all instances of this class
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species = "H. sapiens"
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# Basic initializer, this is called when this class is instantiated.
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# Note that the double leading and trailing underscores denote objects
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# or attributes that are used by python but that live in user-controlled
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# namespaces. Methods(or objects or attributes) like: __init__, __str__,
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# __repr__ etc. are called magic methods (or sometimes called dunder methods)
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# You should not invent such names on your own.
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def __init__(self, name):
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# Assign the argument to the instance's name attribute
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self.name = name
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# Initialize property
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self.age = 0
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# An instance method. All methods take "self" as the first argument
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def say(self, msg):
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return "{name}: {message}".format(name=self.name, message=msg)
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# A class method is shared among all instances
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# They are called with the calling class as the first argument
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@classmethod
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def get_species(cls):
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return cls.species
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# A static method is called without a class or instance reference
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@staticmethod
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def grunt():
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return "*grunt*"
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# A property is just like a getter.
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# It turns the method age() into an read-only attribute
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# of the same name.
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@property
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def age(self):
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return self._age
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# This allows the property to be set
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@age.setter
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def age(self, age):
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self._age = age
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# This allows the property to be deleted
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@age.deleter
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def age(self):
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del self._age
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# Instantiate a class
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i = Human(name="Ian")
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print(i.say("hi")) # prints out "Ian: hi"
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j = Human("Joel")
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print(j.say("hello")) # prints out "Joel: hello"
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# Call our class method
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i.get_species() # => "H. sapiens"
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# Change the shared attribute
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Human.species = "H. neanderthalensis"
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i.get_species() # => "H. neanderthalensis"
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j.get_species() # => "H. neanderthalensis"
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# Call the static method
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Human.grunt() # => "*grunt*"
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# Update the property
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i.age = 42
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# Get the property
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i.age # => 42
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# Delete the property
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del i.age
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i.age # => raises an AttributeError
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####################################################
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## 6. Modules
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## 5. Modules
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####################################################
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# You can import modules
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@ -724,6 +638,189 @@ dir(math)
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# This happens because the local folder has priority
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# over Python's built-in libraries.
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####################################################
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## 6. Classes
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####################################################
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# We use the "class" operator to get a class
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class Human:
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# A class attribute. It is shared by all instances of this class
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species = "H. sapiens"
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# Basic initializer, this is called when this class is instantiated.
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# Note that the double leading and trailing underscores denote objects
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# or attributes that are used by python but that live in user-controlled
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# namespaces. Methods(or objects or attributes) like: __init__, __str__,
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# __repr__ etc. are called magic methods (or sometimes called dunder methods)
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# You should not invent such names on your own.
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def __init__(self, name):
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# Assign the argument to the instance's name attribute
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self.name = name
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# Initialize property
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self.age = 0
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# An instance method. All methods take "self" as the first argument
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def say(self, msg):
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print ("{name}: {message}".format(name=self.name, message=msg))
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# Another instance method
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def sing(self):
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return 'yo... yo... microphone check... one two... one two...'
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# A class method is shared among all instances
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# They are called with the calling class as the first argument
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@classmethod
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def get_species(cls):
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return cls.species
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# A static method is called without a class or instance reference
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@staticmethod
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def grunt():
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return "*grunt*"
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# A property is just like a getter.
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# It turns the method age() into an read-only attribute
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# of the same name.
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@property
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def age(self):
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return self._age
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# This allows the property to be set
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@age.setter
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def age(self, age):
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self._age = age
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# This allows the property to be deleted
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@age.deleter
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def age(self):
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del self._age
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# When a Python interpreter reads a source file it executes all its code.
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# This __name__ check makes sure this code block is only executed when this
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# module is the main program.
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if __name__ == '__main__':
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# Instantiate a class
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i = Human(name="Ian")
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i.say("hi") # "Ian: hi"
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j = Human("Joel")
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j.say("hello") # "Joel: hello"
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# i and j are instances of type Human, or in other words: they are Human objects
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# Call our class method
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i.say(i.get_species()) # "Ian: H. sapiens"
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# Change the shared attribute
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Human.species = "H. neanderthalensis"
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i.say(i.get_species()) # => "Ian: H. neanderthalensis"
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j.say(j.get_species()) # => "Joel: H. neanderthalensis"
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# Call the static method
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print(Human.grunt()) # => "*grunt*"
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print(i.grunt()) # => "*grunt*"
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# Update the property for this instance
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i.age = 42
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# Get the property
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i.say(i.age) # => 42
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j.say(j.age) # => 0
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# Delete the property
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del i.age
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# i.age # => this would raise an AttributeError
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####################################################
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## 6.1 Multiple Inheritance
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####################################################
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# Another class definition
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class Bat:
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species = 'Baty'
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def __init__(self, can_fly=True):
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self.fly = can_fly
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# This class also has a say method
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def say(self, msg):
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msg = '... ... ...'
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return msg
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# And its own method as well
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def sonar(self):
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return '))) ... ((('
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if __name__ == '__main__':
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b = Bat()
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print(b.say('hello'))
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print(b.fly)
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# from "filename-without-extension" import "function-or-class"
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from human import Human
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from bat import Bat
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# Batman inherits from both Human and Bat
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class Batman(Human, Bat):
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# Batman has its own value for the species class attribute
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species = 'Superhero'
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def __init__(self, *args, **kwargs):
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# Typically to inherit attributes you have to call super:
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#super(Batman, self).__init__(*args, **kwargs)
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# However we are dealing with multiple inheritance here, and super()
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# only works with the next base class in the MRO list.
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# So instead we explicitly call __init__ for all ancestors.
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# The use of *args and **kwargs allows for a clean way to pass arguments,
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# with each parent "peeling a layer of the onion".
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Human.__init__(self, 'anonymous', *args, **kwargs)
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Bat.__init__(self, *args, can_fly=False, **kwargs)
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# override the value for the name attribute
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self.name = 'Sad Affleck'
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def sing(self):
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return 'nan nan nan nan nan batman!'
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if __name__ == '__main__':
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sup = Batman()
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# Instance type checks
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if isinstance(sup, Human):
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print('I am human')
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if isinstance(sup, Bat):
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print('I am bat')
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if type(sup) is Batman:
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print('I am Batman')
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# Get the Method Resolution search Order used by both getattr() and super().
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# This attribute is dynamic and can be updated
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print(Batman.__mro__) # => (<class '__main__.Batman'>, <class 'human.Human'>, <class 'bat.Bat'>, <class 'object'>)
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# Calls parent method but uses its own class attribute
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print(sup.get_species()) # => Superhero
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# Calls overloaded method
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print(sup.sing()) # => nan nan nan nan nan batman!
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# Calls method from Human, because inheritance order matters
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sup.say('I agree') # => Sad Affleck: I agree
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# Call method that exists only in 2nd ancestor
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print(sup.sonar()) # => ))) ... (((
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# Inherited class attribute
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sup.age = 100
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print(sup.age)
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# Inherited attribute from 2nd ancestor whose default value was overriden
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print('Can I fly? ' + str(sup.fly))
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####################################################
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## 7. Advanced
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####################################################
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