What does __contains__ do, what can call __contains__ function

Question

Here is my code:

class a(object):
    d=\'ffffd\'
    def __contains__(self):
        if self.d:return True
b=a()
print b.contains(\'d\')  # error
print contai         


        

Answer 1

Lets see a very simple example of magic method __contains__ :

Suppose I have class Player and my __init__ method takes one string argument name. In main I have created an object (obj1) of class Player.

Now if I want to know if my obj1 (in this case attribute name of obj1) contains a particular string, substring or an alphabet, I have to implement __contains__ method as shown in the example.

If my class has __contains__ method I can call built-in operator in on my custom objects as shown in the example.

   class Player():

    def __init__(self, name):
        self.name=name

    def __contains__(self, substring):
        if substring in self.name:
            return True
        else:
            return False

obj1=Player("Sam")
print ('am' in obj1)    ----> True
print ('ami' in obj1)   ----> False