How to Call a method of class having no argument

[dataplumber]

I am trying to call the method of the class having no arguments but it is failing.

class ab:
        def a():
                print("in a")
def b():
        print("in b")

if __name__ == '__main__':
        b()
        ab.a()

Error:
in b
Traceback (most recent call last):
  File "p.py", line 11, in <module>
    ab.a()
TypeError: unbound method a() must be called with ab instance as first argument (got nothing instead)

I have also tried to modify the code as below but not successful

class ab:
        def a():
                print("in a")
def b():
        print("in b")

if __name__ == '__main__':
        b()
        c=ab()
        c.a()

Error:
in b
Traceback (most recent call last):
  File "p.py", line 12, in <module>
    c.a()
TypeError: a() takes no arguments (1 given)