Re: [Python-Dev] Explicitly declaring expected exceptions for ablock

June 21, 2005

      ...
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