[Python-Dev] PEP: Frequently-requested additional features for the `unittest` module

[Scott David Daniels]

Ben Finney wrote:
> Scott David Daniels <Scott.Daniels at Acm.Org> writes:> 
>> I would rather something more like:
>>
>>       def assert_compare_true(op, first, second, msg=None):
>>           if op(first, second):
>>               return
>>           raise self.failure_exception(msg)
>>           if msg is None:
>>               self.failure_exception("%(first)r %(op)r %(second)"
>>                                          % vars())
>>           self.failure_exception("%(first)r %(op)r %(second): %(msg)"
>>                                  % vars())
> I'm confused. It appears to me that your version never gets past the
> first 'raise' statement, which is unconditional; and the rest seems to
> do nothing but instantiate exceptions without using them.

Sorry, I was too hasty last time (had to jet out of the house) and sent
out the unfinished version.  This is what I meant:

      def assert_compare_true(op, first, second, msg=None):
          if op(first, second):
              return
          if msg is None:
              raise self.failure_exception(
                     "%(first)r %(op)r %(second)" % vars())
          raise self.failure_exception(
                     "%(first)r %(op)r %(second): %(msg)" % vars())

(1) Displaying args is the whole point, otherwise just use assert_.
     This form fosters tests that say what is wrong, and not simply
     _that_ something has gone wrong.
     The point is a readable test, reducing boilerplate at the
     call location.  Something like:
          ...
          self.assert_le(sum(source) // len(source), 5, "Mean OK")

(2) No point to doing string conversion except on failure; slow
     __repr__ methods are fine to use if the result is not discarded.

--Scott David Daniels
Scott.Daniels at Acm.Org