[Cython] [cython-users] GSoC 2012

[Stefan Behnel]

Vitja Makarov, 11.03.2012 09:51:
> 2012/3/11 Stefan Behnel:
>> mark florisson, 11.03.2012 07:44:
>>> - better type inference, that would be enabled by default and again
>>> handle thing like reassignments of variables and fallbacks to the
>>> default object type. With entry caching Cython could build a database
>>> of types ((extension) classes, functions, variables) used in the
>>> modules and functions that are compiled (also def functions), and
>>> infer the types used and specialize on those. Maybe a switch should be
>>> added to cython to handle circular dependencies, or maybe with the
>>> distutils preprocessing it can run all the type inference first and
>>> keep track of unresolved entries, and try to fill those in after
>>> building the database. For bonus points the user can be allowed to
>>> write plugins to aid the process.
>>
>> That would be my favourite. We definitely need control flow driven type
>> inference, local type specialisation, variable renaming, etc. Maybe even
>> whole program (or at least module) analysis, like ShedSkin and PyPy do for
>> their restricted Python dialects. Any serious step towards that goal would
>> be a good outcome of a GSoC.
> 
> I think we should be careful here and try to avoid making Cython code
> more complicated.

I agree that WPA is probably way out of scope. However, control flow driven
type inference would allow us to infer the type of a variable in a given
block, e.g. for code like this:

  if isinstance(x, list):
      ...
  else:
      ...

or handle cases like this:

  def test(x):
      x = list(x)
      # ... do read-only stuff with x below this point ...

Here, we currently infer that x is an unknown object that is being assigned
to twice, even though it's obviously a list in all interesting parts of the
function.

Stefan