Failure to build python module with Cython 3.0.0

[marcpaterno]

Cython 3.0.0 was released today. The build of the python module fails with this version of cython because “cpdef” is no longer allowed in the creation of local variables; instead, “cdef” should be used.

Changing all instances of “cpdef” to “cdef” seems to allow the build to success, and the python module resulting can be imported.

[tilmantroester]

I just ran into this as well. For reference, this has been the case since 3.0.0a8: http://docs.cython.org/en/latest/src/changes.html#alpha-8-2021-07-02.

[damonge]

Just to confirm that I've also come across this, and it seems important enough to be fixed!

[lgarrison]

I also ran into this. One trick to work around this in GH Actions is to install the build requirements (including Cython<3) directly into the environment, and then disable pip build isolation:

pip install 'setuptools' 'wheel' 'numpy>=1.19.0' 'Cython>=0.29.21,<3'  # for classy
pip install --no-build-isolation classy

https://github.com/abacusorg/abacusutils/blob/052aa6275276e9b634550992b53d7b62b7e9a929/.github/workflows/tests.yml#L26-L27

[damonge]

After some tinkering, that did the trick. Thanks @lgarrison !
Hope this can be patched soon though!