doctest python

1python -m doctest -v filename.py 

1"""
2This is the "example" module.
3
4The example module supplies one function, factorial().  For example,
5
6>>> factorial(5)
7120
8"""
9
10def factorial(n):
11    """Return the factorial of n, an exact integer >= 0.
12
13    >>> [factorial(n) for n in range(6)]
14    [1, 1, 2, 6, 24, 120]
15    >>> factorial(30)
16    265252859812191058636308480000000
17    >>> factorial(-1)
18    Traceback (most recent call last):
19        ...
20    ValueError: n must be >= 0
21
22    Factorials of floats are OK, but the float must be an exact integer:
23    >>> factorial(30.1)
24    Traceback (most recent call last):
25        ...
26    ValueError: n must be exact integer
27    >>> factorial(30.0)
28    265252859812191058636308480000000
29
30    It must also not be ridiculously large:
31    >>> factorial(1e100)
32    Traceback (most recent call last):
33        ...
34    OverflowError: n too large
35    """
36
37    import math
38    if not n >= 0:
39        raise ValueError("n must be >= 0")
40    if math.floor(n) != n:
41        raise ValueError("n must be exact integer")
42    if n+1 == n:  # catch a value like 1e300
43        raise OverflowError("n too large")
44    result = 1
45    factor = 2
46    while factor <= n:
47        result *= factor
48        factor += 1
49    return result
50
51
52if __name__ == "__main__":
53    import doctest
54    doctest.testmod()
55