[Python-Dev] Explicitly declaring expected exceptions for ablock

[Dmitry Dvoinikov]

> try:
>     c().foo()
> except TypeError:
>     pass
> else:
>     assert False, "c.foo() should have thrown TypeError"


In fact, the above code actually expects foo to throw
particular exception, not exactly the same as the original
requirement. More of

expect TypeError:
       c().foo()

and still can be implemented under PEP 343, that's what
I meant under "more flexible".

Sincerely,
Dmitry Dvoinikov
http://www.targeted.org/

--- Original message follows ---

>> I suspect that you wanted either:

>>    try:
>>        c().foo()
>>        fail('Should have raised TypeError')
>>    except TypeError:
>>        pass  # expected

> Right, of course I use something along these lines:

> try:
>     c().foo()
> except TypeError:
>     pass
> else:
>     assert False, "c.foo() should have thrown TypeError"

> and so if foo throws anything but TypeError I get traceback,
> otherwise it's an assertion error and is reported as such.
> This is probably just one of the many possible wording of the
> same thing though.

> Sincerely,
> Dmitry Dvoinikov
> http://www.targeted.org/

> --- Original message follows ---

>> Dmitry Dvoinikov writes:
>>> The reason for that being self-tests with lots and lots of
>>> little code snippets like this:
>>>
>>> try:
>>>     c().foo()
>>> except TypeError:
>>>     pass

>> Paul Du Boise already responded explaining that PEP 343 probably handles
>> the task you want. I just wanted to mention that you may need to
>> reconsider the task. The above snippet is almost certainly incorrect.
>> I suspect that you wanted either:

>>    try:
>>        c().foo()
>>        fail('Should have raised TypeError')
>>    except TypeError:
>>        pass  # expected

>> or perhaps this:

>>     try:
>>         c().foo()
>>     except TypeError:
>>         fail('Should not have raised TypeError')

>> There ARE situations when you want to allow an exception (but not
>> necessarily expect it) and do nothing when it occurs, but I don't
>> find them all that common, and I certainly don't find them arising
>> in unit tests.

>> -- Michael Chermside

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