[python3/en] Add single inheritance section

This commit is contained in:
Keith Miyake 2017-10-19 22:26:32 -07:00
parent 4d3637bfc4
commit 9b6d84309c

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@ -669,7 +669,7 @@ class Human:
# An instance method. All methods take "self" as the first argument # An instance method. All methods take "self" as the first argument
def say(self, msg): def say(self, msg):
print ("{name}: {message}".format(name=self.name, message=msg)) print("{name}: {message}".format(name=self.name, message=msg))
# Another instance method # Another instance method
def sing(self): def sing(self):
@ -740,7 +740,101 @@ if __name__ == '__main__':
#################################################### ####################################################
## 6.1 Multiple Inheritance ## 6.1 Inheritance
####################################################
# Inheritance allows new child classes to be defined that inherit methods and
# variables from their parent class.
# Using the Human class defined above as the base or parent class, we can
# define a child class, Superhero, which inherits the class variables like
# "species", "name", and "age", as well as methods, like "sing" and "grunt"
# from the Human class, but can also have its own unique properties.
# To take advantage of modularization by file you could place the classes above in their own files,
# say, human.py
# To import functions from other files use the following format
# from "filename-without-extension" import "function-or-class"
from human import Human
# Specify the parent class(es) as parameters to the class definition
class Superhero(Human):
# If the child class should inherit all of the parent's definitions without
# any modifications, you can just use the "pass" keyword (and nothing else)
# but in this case it is commented out to allow for a unique child class:
# pass
# Child classes can override their parents' attributes
species = 'Superhuman'
# Children automatically inherit their parent class's constructor including
# its arguments, but can also define additional arguments or definitions
# and override its methods such as the class constructor.
# This constructor inherits the "name" argument from the "Human" class and
# adds the "superpower" and "movie" arguments:
def __init__(self, name, movie=False,
superpowers=["super strength", "bulletproofing"]):
# add additional class attributes:
self.fictional = True
self.movie = movie
self.superpowers = superpowers
# The "super" function lets you access the parent class's methods
# that are overwritten by the child, in this case, the __init__ method.
# This calls the parent class constructor:
super().__init__(name)
# overload the sing method
def sing(self):
return 'Dun, dun, DUN!'
# add an additional class method
def boast(self):
for power in self.superpowers:
print("I wield the power of {pow}!".format(pow=power))
if __name__ == '__main__':
sup = Superhero(name="Tick")
# Instance type checks
if isinstance(sup, Human):
print('I am human')
if type(sup) is Superhero:
print('I am a superhero')
# Get the Method Resolution search Order used by both getattr() and super()
# This attribute is dynamic and can be updated
print(Superhero.__mro__) # => (<class '__main__.Superhero'>,
# => <class 'human.Human'>, <class 'object'>)
# Calls parent method but uses its own class attribute
print(sup.get_species()) # => Superhero
# Calls overloaded method
print(sup.sing()) # => Dun, dun, DUN!
# Calls method from Human
sup.say('Spoon') # => Tick: Spoon
# Call method that exists only in Superhero
sup.boast() # => I wield the power of super strength!
# => I wield the power of bulletproofing!
# Inherited class attribute
sup.age = 31
print(sup.age) # => 31
# Attribute that only exists within Superhero
print('Am I Oscar eligible? ' + str(sup.movie))
####################################################
## 6.2 Multiple Inheritance
#################################################### ####################################################
# Another class definition # Another class definition
@ -766,20 +860,16 @@ if __name__ == '__main__':
print(b.fly) print(b.fly)
# To take advantage of modularization by file you could place the classes above in their own files, # To take advantage of modularization by file you could place the classes above in their own files,
# say, human.py and bat.py # say, superhero.py and bat.py
# To import functions from other files use the following format # To import functions from other files use the following format
# from "filename-without-extension" import "function-or-class" # from "filename-without-extension" import "function-or-class"
# superhero.py # superhero.py
from human import Human from superhero import Superhero
from bat import Bat from bat import Bat
# Batman inherits from both Human and Bat # Batman inherits from both Superhero and Bat
class Batman(Human, Bat): class Batman(Superhero, Bat):
# Batman has its own value for the species class attribute
species = 'Superhero'
def __init__(self, *args, **kwargs): def __init__(self, *args, **kwargs):
# Typically to inherit attributes you have to call super: # Typically to inherit attributes you have to call super:
@ -789,7 +879,8 @@ class Batman(Human, Bat):
# So instead we explicitly call __init__ for all ancestors. # So instead we explicitly call __init__ for all ancestors.
# The use of *args and **kwargs allows for a clean way to pass arguments, # The use of *args and **kwargs allows for a clean way to pass arguments,
# with each parent "peeling a layer of the onion". # with each parent "peeling a layer of the onion".
Human.__init__(self, 'anonymous', *args, **kwargs) Superhero.__init__(self, 'anonymous', movie=True,
superpowers=['Wealthy'], *args, **kwargs)
Bat.__init__(self, *args, can_fly=False, **kwargs) Bat.__init__(self, *args, can_fly=False, **kwargs)
# override the value for the name attribute # override the value for the name attribute
self.name = 'Sad Affleck' self.name = 'Sad Affleck'
@ -802,8 +893,8 @@ if __name__ == '__main__':
sup = Batman() sup = Batman()
# Instance type checks # Instance type checks
if isinstance(sup, Human): if isinstance(sup, Superhero):
print('I am human') print('I am a superhero)
if isinstance(sup, Bat): if isinstance(sup, Bat):
print('I am bat') print('I am bat')
if type(sup) is Batman: if type(sup) is Batman:
@ -811,10 +902,13 @@ if __name__ == '__main__':
# Get the Method Resolution search Order used by both getattr() and super(). # Get the Method Resolution search Order used by both getattr() and super().
# This attribute is dynamic and can be updated # This attribute is dynamic and can be updated
print(Batman.__mro__) # => (<class '__main__.Batman'>, <class 'human.Human'>, <class 'bat.Bat'>, <class 'object'>) print(Batman.__mro__) # => (<class '__main__.Batman'>,
# => <class 'superhero.Superhero'>,
# => <class 'human.Human'>,
# => <class 'bat.Bat'>, <class 'object'>)
# Calls parent method but uses its own class attribute # Calls parent method but uses its own class attribute
print(sup.get_species()) # => Superhero print(sup.get_species()) # => Superhuman
# Calls overloaded method # Calls overloaded method
print(sup.sing()) # => nan nan nan nan nan batman! print(sup.sing()) # => nan nan nan nan nan batman!
@ -827,10 +921,10 @@ if __name__ == '__main__':
# Inherited class attribute # Inherited class attribute
sup.age = 100 sup.age = 100
print(sup.age) print(sup.age) # => 100
# Inherited attribute from 2nd ancestor whose default value was overridden. # Inherited attribute from 2nd ancestor whose default value was overridden.
print('Can I fly? ' + str(sup.fly)) print('Can I fly? ' + str(sup.fly)) # => Can I fly? False