如果模块的版本不正确，应该抛出哪个异常？

Question

This may have been asked before or I may be overly pedantic, but my own searches have come up empty.

Looking through the Python 2.x exceptions page , I'm not sure which one I should raise if my script determines that the __version__ of a module that's been imported, eg cv2 , is not the correct version. For example, a script I'm working on requires OpenCV version 3; what's the best exception to raise in the following block if it determines that the version != 3?

import cv2
if not cv2.__version__.startswith('3'):
    raise ValueError('OpenCV _3_ required')

Answer 1

You can create you own custom exception if the existing ones don't suffice.

class VersionError(Exception):
    def __init__(self, msg):
        Exception.__init__(self,msg) 

Answer 2

You've got a lot of options depending on what you want to do with this exception... Generally, I'd expect the install scripts to handle setting up the appropriate versions of dependencies so I might think of this as a simple runtime assertion -- Therefore AssertionError may be appropriate.

This one is really nice -- You don't need an if statement, just an assert :

assert cv2.__version__.startswith('3'), 'OpenCV _3_ required'

My next bet would be to use RuntimeError as that is really meant to be a general exception that happens at runtime (and isn't usually meant to be caught)... It's a pretty general "Oh snap, something bad happened that we cannot recover from. Lets just spit out an error to let the user know what happened".