Compatibility with cython3

[mglisse]

Compatibility with cython3

[mglisse]

This handling of __ is a general Python thing: https://docs.python.org/3/tutorial/classes.html#private-variables

In [1]: class A:
   ...:     def __x(self):
   ...:         return True
   ...: a = A()
   ...: a.__x()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In [1], line 5
      3         return True
      4 a = A()
----> 5 a.__x()

AttributeError: 'A' object has no attribute '__x'

In [2]: a._A__x()
Out[2]: True

[VincentRouvreau]

A reminder on this #777 (comment)

[mglisse]

It seems that the only issue is using the functions __is_defined() and __is_persistence_defined() in tests. @VincentRouvreau , what do you prefer?

1. remove the assertions on those 2 functions from the tests
2. rename them so they start with a single underscore
3. on the day we switch to cython3, update the tests to _SimplexTree__is_defined, etc
4. other

I think I am in favor of option 2 (it is simple, compatible with both versions of cython, and I don't think the protection offered by the double underscore is that important here, but I could be wrong). We could also remove one underscore from persistence_graphical_tools.__min_birth_max_death while we are at it.

[mglisse]

Cython3 is now out, and at least one macosx+windows CI job already uses it and fails (the exception specifications don't match)

/Users/runner/work/gudhi-devel/gudhi-devel/src/python/gudhi/simplex_tree.pyx:613:65: Cannot assign type 'bool (vector[int], void *) except? -1' to 'blocker_func_t'