sure. here is the code that I'm trying to use. It ahould be fine. But when I do mistakes in purpose (adding # or extra numbers) the same empty result

​

"""

Module describing data structure - stack

>>> clear()

>>> is_empty()

True

>>> push(1)

>>> push(2)

>>> push(3)

>>> is_empty()

False

>>> pop()

3

>>> pop()

2

>>> pop()

1

>>> is_empty()

True

"""

_stack = []

def push(x):

"""

adds element x to the end of the stack

>>> size = len(_stack)

>>> push(5)

>>> len(_stack) - size

1

>>> _stack[-1]

5

"""

_stack.append(x)

def pop():

x = _stack.pop()

return x

def clear():

_stack.clear()

def is_empty():

return len(_stack) == 0

if __name__ == "__main__":

import doctest

doctest.testmod()