pythonize cython code

[jbrockmendel]

Use python-style type annotations instead of cython-style in a few places.

Use python-style isinstance checks in cases where cython will automatically optimize them into C calls.

Part of the hope is that we can get the code close enough to valid python that we can trick flake8 into working on it.

[jbrockmendel]

These two are not used within cython, I think they were cpdef just because with the other syntax you can’t declare a return type with just def.

[codecov]

Codecov Report

Merging #22638 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #22638   +/-   ##
=======================================
  Coverage   92.17%   92.17%           
=======================================
  Files         169      169           
  Lines       50708    50708           
=======================================
  Hits        46740    46740           
  Misses       3968     3968

Flag	Coverage Δ
#multiple	90.58% <ø> (ø)	⬆️
#single	42.35% <ø> (ø)	⬆️

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[jreback]

thanks. maybe add a note somewhere that we can use type annotation in cython files (maybe at the top of each file?)

[jorisvandenbossche]

Use python-style type annotations instead of cython-style in a few places.

Sorry, why do we think this is an improvement? Now we have two ways of doing things?
Can you provide a bit more background / reasoning?

[jbrockmendel]

Some discussion in #22180.

Main motivation: I think that if we can get the code close enough to valid python, we can trick flake8 into running on it.