The difference between python class methods and ordinary methods

The difference between python class methods and ordinary methods

The following uses examples to illustrate the differences.

First, define a class, including 2 methods:

class Apple(object):
        def get_apple(self, n):
                print "apple: %s,%s" % (self,n)
        @classmethod
        def get_class_apple(cls, n):
                print "apple: %s,%s" % (cls,n)

Common methods of the class

Common methods of the class need to be called by instances of the class .

a = Apple()
a.get_apple(2)

Output results

apple: <__main__.Apple object at 0x7fa3a9202ed0>,2

Look at the binding relationship:

print (a.get_apple)
<bound method Apple.get_apple of <__main__.Apple object at 0x7fa3a9202ed0>>

The ordinary methods of the class can only be used with instances of the class. If you use a class to call a normal method, the following error occurs:

Apple.get_apple(2)
Traceback (most recent call last): File "static.py", line 22, in <module> Apple.get_apple(2) TypeError: unbound method get_apple() must be called with Apple instance as first argument (got int instance instead)

Class method

Class method means that the method is bound to the class.

a.get_class_apple(3)
Apple.get_class_apple(3)
apple: <class &#39;__main__.Apple&#39;>,3
apple: <class &#39;__main__.Apple&#39;>,3

Look at the binding relationship again:

print (a.get_class_apple) print (Apple.get_class_apple)

The output results are the same when using instances and calling classes.

<bound method type.get_class_apple of <class &#39;__main__.Apple&#39;>> <bound method type.get_class_apple of <class &#39;__main__.Apple&#39;>>

Related recommendations: "Python Tutorial"

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