def add(x, y):
    """ add two number or string
    >>> add(1, 2)
    3

    >>> add("hello", " world")
    'hello world'

    >>> add(1, 2.0)
    3

    >>> add("hello", " python")  # doctest: +ELLIPSIS
    'hello ...'

    """
    return x+y


if __name__ == '__main__':
    import doctest
    doctest.testmod()

Trying:
    add(1, 2)
Expecting:
    3
ok
Trying:
    add("hello", " world")
Expecting:
    'hello world'
ok
Trying:
    add(1, 2.0)
Expecting:
    3
**********************************************************************
File "doctest_sample.py", line 13, in __main__.add
Failed example:
    add(1, 2.0)
Expected:
    3
Got:
    3.0
Trying:
    add("hello", " python")  # doctest: +ELLIPSIS
Expecting:
    'hello ...'
ok
1 items had no tests:
    __main__
**********************************************************************
1 items had failures:
   1 of   4 in __main__.add
4 tests in 2 items.
3 passed and 1 failed.
***Test Failed*** 1 failures.