def assert_false():
    assert False, 'False!'

def invert(x):
    """Return 1/x

    >>> invert(2)
    Never printed if x is 0
    0.5
    """
    result = 1/x  # Raises a ZeroDivisionError if x is 0
    print('Never printed if x is 0')
    return result

def invert_safe(x):
    """Return 1/x, or the string 'divison by zero' if x is 0.

    >>> invert_safe(2)
    Never printed if x is 0
    0.5
    >>> invert_safe(0)
    'division by zero'
    """
    try:
        return invert(x)
    except ZeroDivisionError as e:
        return str(e)