从另一个包导入Cython标头

Question

I have a package called A :

A/
  __init__.py
  _test.pyx

I have the source for another package called B :

B/
  __init__.py
  _wrapper.pxd
  _other.pxd
  _other.pyx

_wrapper.pxd wraps a C library. I'd like to cimport _wrapper.pxd in A/_test.pyx

So I do this in _test.pyx :

from B cimport _wrapper

my setup.py looks like this:

ext_modules = cythonize([
           Extension("A._test", ["src/A/_test.pyx"], include_dirs=["/path/to/B", "."])])

When I compile I get B.pxd not found followed by a bunch of errors.

How can I import a cython module from another package into my package?

Answer 1

Short answer

In order to cimport .pxd files from other packages you need to give your package a __init__. pxd file. Then you can treat your package B as a cython package and do not need to worry about include paths.

Reproduction

I tried to reproduce the error like this:

setup.py
  A/
    __init__.py
    _test.pyx
  B/
    __init__.py
    _wrapper.pxd
    _other.pxd
    _other.pyx

_wrapper.pxd

from distutils.core import Extension, setup
from Cython.Build import cythonize

ext_modules = cythonize([
        Extension("A._test", ["A/_test.pyx"])])
setup(ext_modules=ext_modules)

_test.pyx

 from B cimport _wrapper cpdef bar(): _wrapper.foo() 

setup.py

$ touch B/__init__.pxd

setup.py
  A/
    __init__.py
    _test.pyx
  B/
    __init__.pxd
    _wrapper.pxd
    _other.pxd
    _other.pyx

$ python setup.py build_ext --inplace
$ ipython

In [1]: from A import _test

In [2]: _test.bar()
42

And it did not work with this error:

 A/_test.pyx: cannot find cimported module 'B' Compiling A/_test.pyx because it changed. [1/1] Cythonizing A/_test.pyx Error compiling Cython file: ------------------------------------------------------------ ... from B cimport _wrapper ^ ------------------------------------------------------------ A/_test.pyx:1:0: 'B.pxd' not found Error compiling Cython file: [...] 

This should be what you faced.

How to solve this

For me, adding an empty __init__.pxd file solved the problem. I did not need to specify an include path or have a __init__.py and used the files as listed above. All files which are not shown above I kept empty.

 $ touch B/__init__.pxd setup.py A/ __init__.py _test.pyx B/ __init__.pxd _wrapper.pxd _other.pxd _other.pyx $ python setup.py build_ext --inplace $ ipython In [1]: from A import _test In [2]: _test.bar() 42 

I hope this works for you.

Alternative

If it is an option, consider moving the _wrapper.pxd to the A folder. Then you can directly use:

 cimport _wrapper 

I guess you would like to preserve the package structure as you have laid it out, so this is just here for completeness sake.