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

[Victor Stinner]

Python has test_dynamic which tests such corner cases.

For example, test_modify_builtins_while_generator_active(): "Modify
the builtins out from under a live generator."
https://hg.python.org/cpython/file/58266f5101cc/Lib/test/test_dynamic.py#l49

Victor

2016-01-27 10:28 GMT+01:00 Paul Moore <p.f.moore at gmail.com>:
> 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         assert value == 3 + 97, "Outdated `len` used."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         assert value == 3 + 97, "Outdated `len` used."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         assert module_a.test_func(callback) == 3 + 97, "Outdated `len` used."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