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

to get your code to do something (although nothing useful):

class a(object):

    d = 'ffffd'

    def __contains__(self, m):
        if self.d: 
            return True

b = a()

>>> 'd' in b
True

The docs.