with statement work on class

Question

{class foo(object):
    def __enter__ (self):
        print(\"Enter\")
    def __exit__(self,type,value,traceback):
        print(\"Exit\")
    def method(self):
            


        

Answer 1

The problem is that your __enter__ method does not return self.

Answer 2

__enter__ should return self:

class foo(object):
    def __enter__ (self):
        print("Enter")
        return self
    def __exit__(self,type,value,traceback):
        print("Exit")
    def method(self):
        print("Method")
with foo() as instant:
    instant.method()

yields

Enter
Method
Exit

If __enter__ does not return self, then it returns None by default. Thus, instant is assigned the value None. This is why you get the error message

'NoneType' object has no attribute 'method'

(my emphasis)