I don't know the difference between class variables and instance variables. Can anybody give me an example?
Thank you so much:)
Here you have an example of a class name Animal and some instance names (dog, cat, cow) ...
class Animal: """ class names by convention are capitalized """ # category is global to the class and is available to all # instances of class Animal category = "animal" def __init__(self, animal, sound): """ __init__() is the 'constructor' of the class instance when you create an instance of Animal you have to supply it with the name and the sound of the animal 'self' refers to the instance if the instance is dog, then name and sound will be that of the dog 'self' also makes name and sound available to all the methods within the class """ self.name = animal self.sound = sound def speak(self): """ the first argument of a class method is always self this method needs to be called with self.speak() within the class, or the instance_name.speak() outside the class """ print( "The %s goes %s" % (self.name, self.sound) ) # create a few class instances # remember to supply the name and the sound for each animal dog = Animal("dog", "woof") cat = Animal("cat", "meeouw") cow = Animal("cow", "mooh") # testing ... # now you can call each animals function/method speak() # by simply connecting instance_name and speak() with a '.' cow.speak() cat.speak() dog.speak() # you can also access variables associated with the instance # since cow is the instance # self.sound becomes cow.sound print(cow.sound) # category is a class variable common to all istances print(dog.category) print(cat.category) print(cow.category) """my result --> The cow goes mooh The cat goes meeouw The dog goes woof mooh animal animal animal """
According to advice from The_Kernel (thanks)
category" is considered a class variable,
self.name and self.sound are instance variables.
A class variable is shared across instances of the class, while an instance variable is unique to that instance of the class. Consider the following example:
class Foo: name = "FOO" def __init__(self, value): self.value = value mine = Foo("bar") mine_2 = Foo("taz") print mine.value, mine.name print mine_2.value, mine.name Foo.name = "BAR" print mine.value, mine.name print mine_2.value, mine.name #output is: # bar FOO # taz FOO # bar BAR # taz BAR
thx guys i understood