[Python-3000] Interaction between unittest and keyword argument machinery

[Guido van Rossum]

On 3/6/07, Patrick Maupin <pmaupin at gmail.com> wrote:
> It appears that if a C function is called from Python with **kwargs, a
> new dictionary object is created and passed to the C function even if
> **kwargs is empty, but if the same C function is called without
> **kwargs, then the NULL pointer is passed to the C function.
>
> Because unittest always creates **kwargs, any code path in a C
> function which is only executed when the *keywords parameter is NULL
> will never be correctly tested from the standard unittest methods.

This needs some context; which call from unittest to a C function are
you talking about?

> doctest doesn't have this issue, but appears to be deprecated.

Far from it! Doctest is alive and well. I even used it to test the
xreload module I added to Py3k. I admit that I've not been a fan of it
in the past, and in many cases I will prefer unittest, but there are
definitely very good reasons to support doctest. Consider it a rare
deviation from TOOWTDI.

> OTOH
> unless it would be a major performance hit to never pass empty
> *dictionary parameters (always use a NULL pointer) to C functions, it
> would remove a whole class of untested potential execution paths to
> change the interpreter.

You guessed it, it's a major performance hit to create a whole new
dict object (even if empty) when the majority of calls don't need it.
So, no, this isn't going away any time soon.

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)