[PYTHON] If you have trouble importing between folders when creating a package with Cython, see this.

Overview

When I was trying to make a package by writing setup.py etc. in Cython Basically, I feel that the folder structure is chaotic. The reason is that when wrapping C ++ with Cython, the part that wraps the implementation on the C ++ side must copy the code of the header on the C ++ side to Cython as well.

This will increase the number of files and you will have to separate the folders. At this time, if you don't understand the meaning of __init__.py or why you put it (for me), you'll get stuck.

What seems to be the best

Since there is a lot of source code, it is good to divide it into various folders, pyxFrom filepxdfilecimportand when, And when `` `pxdfiles are cimport``` across folders You may get an error like "File not found".

To avoid wasting time with such errors I think it would be better to do this.

--C ++ and Cython code are separated by folders --When the folder containing Cython code has subdirectories, put `__init__.py``` in each. --Write all `cimport``` in Cython code with the path seen from the project's parent directory (where setup.py is located).

Folder structure

For example, make a folder structure like this.

setup.py

cpp_code/*

cython_code/
        | -- __init__.py
      folder_a
        | -- __init__.py
        | -- test_a.pyx
        | -- test_a.pxd
      folder_b
        | -- __init__.py
        | --  test_b.pyx
        | --  test_b.pxd
        

In such a case, put __ init__.py in each folder and put it. For example, if test_b.pxd wants to import test_a.pxd```,

test_b.pxd

from cython_code.folder_a.test_a cimport *

If you write it in a unified way like this, you probably won't have to worry too much about import errors.

I summarized it as a memorandum.

end.