Python Koan 131 引发异常

Question

这几天通过做Python Koans来学习Python，遇到了Python中引发异常的问题。具体来说，在看完公案之后，我什至对 try... except... 感到困惑。我知道鲁迪·科恩 (Rudy Koan) 也有类似的问题 Ruby Koan 151 raising exceptions 。但我是一个Python新手，对Ruby一无所知。

所以这是公案:

# You need to finish implementing triangle() in the file 'triangle.py'
from triangle import *

class AboutTriangleProject2(Koan):
    # The first assignment did not talk about how to handle errors.
    # Let's handle that part now.
    def test_illegal_triangles_throw_exceptions(self):
        # Calls triangle(0, 0, 0)
        self.assertRaises(TriangleError, triangle, 0, 0, 0)

        self.assertRaises(TriangleError, triangle, 3, 4, -5)
        self.assertRaises(TriangleError, triangle, 1, 1, 3)
        self.assertRaises(TriangleError, triangle, 2, 4, 2) 

下面是triangle.py

def triangle(a, b, c):
    # DELETE 'PASS' AND WRITE THIS CODE

    if a == b and b == c and c == a:
        return 'equilateral'
    if a == b or b == c or a == c:
        return 'isosceles'
    else:
        return 'scalene'

# Error class used in part 2.  No need to change this code.
class TriangleError(StandardError):
    pass

我应该完成triangle()函数。

据我了解，try... except... 的功能类似于如果满足某些条件则执行某些操作，否则会出现异常。那么在我的情况下，我应该使用 if ... then raise TriangleError 还是 try... except ... ？它们之间有什么区别？

非常感谢!

Answer 1

请参阅以下答案:

def triangle(a, b, c):
    # DELETE 'PASS' AND WRITE THIS CODE
    if min([a,b,c])<=0:
        raise TriangleError
    x,y,z = sorted([a,b,c])
    if x+y<=z:
        raise TriangleError
    if a==b and b==c and c==a:
        return 'equilateral'
    if a==b or b==c or a==c:
        return 'isosceles'
    else:
        return 'scalene'