[Python-Dev] FAT Python (lack of) performance

[Paul Moore]

On 27 January 2016 at 05:23, Sjoerd Job Postmus <sjoerdjob at sjec.nl> wrote:
> On Mon, Jan 25, 2016 at 11:58:12PM +0100, Victor Stinner wrote:
>> ...
>> Oh, they are a lot of things to do! ...
>
> Just wondering, do you also need a set of (abusive) test-cases which
> check 100% conformity to the CPython semantics? I'm sure many of us
> would be able to whip up some ideas of things that are possible with
> Python and are of the kind "but you should not do that! That's bad
> programming!" which may or may not break the optimizations (especially
> specialized functions).
>
> I'm thinking of things like
>
>     def override_length_function_test():
>         global len
>         value = len("abc")
>         len = lambda obj: ord(obj[0]))
>         value += len("abc")
>         assert value == 3 + 97, "Outdated `len` used."
>
> And also cases where `len` was changed not in the function itself, but
> in another function that was called indirectly (maybe 4 functions down,
> one of which was monkey-patched in after the compilation step):
>
>     module_a.py
>     def test_func(callback):
>         value = len("abc")
>         callback()
>         value += len("abc")
>         assert value == 3 + 97, "Outdated `len` used."
>
>     module_b.py
>     import module_a
>     def override_length_function_test():
>         def callback():
>             module_a.len = lambda obj: ord(obj[0])
>         assert module_a.test_func(callback) == 3 + 97, "Outdated `len` used."
>
> (I'm sure some of the other readers of this list can be even more
> creative in trying to show that making optimizations like this can break
> semantics.)
>
> Other fun tricks I'd like to try is overriding the `len` method from a
> signal handler, what happens when you monkey-patch a dependent method,
> having `__getitem__` and `__getattr__` on some value override `len`.
>
> Basically: trying things that I normally should not try during my
> working hours, on account of wanting to still have a job the next day.
>
> Kind regards,
> Sjoerd Job

Maybe I'm just nasty, but IMO those kinds of "torture tests" are just
as valuable in general, so I'd encourage people to submit patches to
the main Python test suite to add them.

Paul