Inner class function without self

Question

Peace, everyone! I\'m using Python 3.6.3 and I find strange that such construction is possible:

class TestClass(object):
    def __init__(self):
        self         


        

Answer 1

Let me explain with an example:

class TestClass(object):
  def __init__(self):
    self.arg = "arg"

  def test1():
    print("class method test1, Hey test")

  @classmethod
  def test2(cls):
    print("class method test2, Hey test")

  def test3(self):
    print("instance method test3, Hey test")

Look what happens when you call test1 with the class or with the instance:

First:

  TestClass.test1() #called from class
class method test1, Hey test
   TestClass().test1() #created an instance TestClass()
Traceback (most recent call last):
  File "python", line 1, in 
TypeError: test1() takes 0 positional arguments but 1 was given

that's because when you create an instance, the self parameter is used, but here, the method has not the self parameter, that's why it brakes.

next one!

   TestClass.test2()
class method test2, Hey test
   TestClass().test2()
class method test2, Hey test

That worked for instance and for class, why? well, as you can see test2(cls) take an argument, cls, here, I'm not using it, so, it's ok that it works.

bring me the next subject, muajaja

  TestClass().test3()
instance method test3, Hey test
   TestClass.test3()
Traceback (most recent call last):
  File "python", line 1, in 
TypeError: test3() missing 1 required positional argument: 'self'

That's easy to see, when you call it as class, you haven't provided the self parameter