原来>>>后面要加一个空格。。之前一直报错我都感到莫名其妙！

# -*- coding: utf-8 -*-

def fact(n):
    '''
    >>> fact(1)
    1
    >>> fact(2)
    2
    >>> fact(5)
    120
    >>> fact(0)
    Traceback (most recent call last):
    ...
    ValueError
    '''
    if n<1:
        raise ValueError()
    if n==1:
        return 1
    return n*fact(n-1)

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