class Enemy:
    life = 3

    def attack(self):
        print('ouch!')
        self.life -= 1

    def checkLife(self):
        if self.life <= 0:
            print('I am dead')
        else:
            print(str(self.life) + "life left")


enemy1 = Enemy
enemy1.attack()
enemy1.checkLife()

C:UsersLiamAppDataLocalProgramsPythonPython36-32python.exe C:/Users/Liam/PycharmProjects/YouTube/first.py
Traceback (most recent call last):
  File "C:/Users/Liam/PycharmProjects/YouTube/first.py", line 16, in <module>
    enemy1.attack()
TypeError: attack() missing 1 required positional argument: 'self'

Process finished with exit code 1

enemy1 = Enemy()
enemy1.attack()
enemy1.checkLife()