Can Python assert be used to check for specific exceptions in a function? For instance, if I have a function that I know will raise a KeyError, can assert detect it? For example:
def get_value(x): lookup = {'one': 1} return lookup[x] assert get_value('two') == KeyError When I run this I just get the KeyError exception. Can assert check something like this? Or is that not what assert is used for?
See this: What is the use of "assert" in Python?
assert is for asserting a condition, means verify that this condition has been met else trigger an action. For your use case, you want to catch an exception, so this is something you want.
#!/usr/bin/env python import sys def get_value(x): lookup = {'one': 1} return lookup[x] try: get_value('two') except: # catch *all* exceptions e = sys.exc_info() print e This will catch the exception and print it. In this particular case it will print something like: (<type 'exceptions.KeyError'>, KeyError('two',), <traceback object at 0x102c71c20>)
type()in this case.assert_raises.tryif you wanted to manually catch the error; the function doesn't return the error, it raises it.assertonly works if__debug__is True), not runtime errors or conditions that may or may not arise, or other special events. For those (thinkExceptions) use atryblock