Python面向对象的编程允许在类级别或实例级别使用变量，其中变量只是表示您在程序中使用的值的符号。
在类级别，变量称为类变量，而在实例级别的变量称为实例变量。让我们通过一个简单的示例了解类变量和实例变量-
# Class Shark
class Shark:
animal_type= 'fish' # Class Variable
def __init__(self, name, age):
self.name = name
self.age = age
# Creating objects of Shark class
obj1 = Shark("Jeeva", 54)
obj2 = Shark("Roli", 45)
print ("Printing class variable using two instances")
print ("obj1.animal_type =", obj1.animal_type)
print ("obj2.animal_type =", obj2.animal_type)
#Let's change the class variable using instance variable
obj1.animal_type = "BigFish"
print ("\nPrinting class variable after making changes to one instance")
print ("obj1.animal_type=", obj1.animal_type)
print ("obj2.animal_type =", obj2.animal_type)在上面的程序中，我们创建了一个Shark类，然后尝试使用object更改class变量，这将为该特定对象创建一个新的实例变量，并且此变量遮盖了class变量。
Printing class variable using two instances obj1.animal_type = fish obj2.animal_type = fish Printing class variable after making changes to one instance obj1.animal_type= BigFish obj2.animal_type = fish
让我们修改上面的程序，以获得正确的输出-
# Class Shark
class Shark:
animal_type= 'fish' # Class Variable
def __init__(self, name, age):
self.name = name
self.age = age
# Creating objects of Shark class
obj1 = Shark("Jeeva", 54)
obj2 = Shark("Roli", 45)
print ("Printing class variable using two instances")
print ("obj1.animal_type =", obj1.animal_type)
print ("obj2.animal_type =", obj2.animal_type)
#Let's change the class variable using instance variable
#obj1.animal_type = "BigFish"
Shark.animal_type = "BigFish"
print("New class variable value is %s, changed through class itself" %(Shark.animal_type))
print ("\nPrinting class variable after making changes through instances")
print ("obj1.animal_type=", obj1.animal_type)
print ("obj2.animal_type =", obj2.animal_type)Printing class variable using two instances obj1.animal_type = fish obj2.animal_type = fish New class variable value is BigFish, changed through class itself Printing class variable after making changes through instances obj1.animal_type= BigFish obj2.animal_type = BigFish