Cython C-level Interface Of Package: *.pxd Files Are Not Found

In a nutshell I try to compile a cython extension called extension2 that cimports a file extension from a self-created package. When building extension2, I get the error that exte

Solution 1:

Cython does not support implicit namespace packages as of yet. That is, cython searches only subdirectories that contain a file init.*, whereby * can be anything from py, pyc, pyx, and pxd.

I have created a bugtracker report for this issue, in case you want to follow up on whether the issue has been fixed in a newer version yet (I worked with Cython 0.29.14).

Until then, a workaround is to create an empty file __init__.pxd in the folder nsp. This file should be ignored by python, as it is not a *.py file, and lets cython search the subdirectories for packages. The file structure then reads as follows:

├── nsp
│   ├── __init__.pxd
│   └── A
|       ├── extension.pxd
|       ├── extension.pyx
│       └── __init__.py
└── setup.py

To install the additional file __init__.pxd in the namespace package, change the packages argument of setup(...) to packages=['nsp', 'nsp.A'] and the package_data argument to package_data={'': ['*.pxd', '*.pyx']}.

Edit:

The bug has been known to the cython developers and will be fixed in version 3. See Fix for cimport from PEP420 namespace.