TestClass.py

class TestClass:
    def __init__(self, someString):
        self.someString = someString # an instance variable
    
    def test():
        print('Test')
        
# uppon creating an instance of TestClass called obj0
# the special function __init__ is called
# in this function obj0 is passed as an argument named self
# and a string is also passed named someString
obj0 = TestClass('some string')

# the operation bellow isn't valid because obj0 will be passed as an argument into the method test
# however, as seen in the definition of test, the method test does not define any parameter.
obj0.test() # comment this line after you see the error it produces

# in order to call the method test, we either have to define it with at least one parameter
# conventionally called self
# or we can call it from the class itself
# however, it won't be able to access any instance variable this way
TestClass.test()