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Pure-Python compatible "not None", "const" #2695

jbrockmendel opened this Issue Nov 1, 2018 · 1 comment


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jbrockmendel commented Nov 1, 2018

Three goals are currently coming into conflict:

  • wanting to move code from ndarray[foo_t] to foo_t[:]
  • needing to reject None and allow read-only arrays
  • wanting to move towards valid-python

The first two I can accomplish with const foo_t[:] not None, but that blows the third out of the water. Any thoughts on syntax (decorators?) to accomplish this in pure python mode?


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scoder commented Nov 1, 2018

Regarding not None, this can be done with an explicit None check in both Python and Cython. I don't think we should create any special semantics here. (But I created #2696 anyway, just to keep it in mind.)

It's true that const is not currently available as a pure Python type modifier. Not sure how difficult that is, given that it's a plain modifier in C, but would have to be a function in Python, like

def func(data: cython.const([:]): ...

Requiring a typedef() here seems a bit overkill.
Worth trying out, in any case. PR welcome.

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