Python package with cython extension get import error

Question

I want to make python package with C extensions. I want this to be done with cython. My structure is:

.
├── build
│   ├── lib.linux-i686-2.7
│   │   └── pyA13SOM
│   │       ├── cython
│   │       │   └── spi.so
│   │       └── __init__.py
│   └── temp.linux-i686-2.7
│       └── pyA13SOM
│           └── cython
│               ├── my_test.o
│               └── spi.o
├── CHANGES.txt
├── Makefile
├── MANIFEST
├── pyA13SOM
│   ├── cython
│   │   ├── clibraries
│   │   │   └── spi_test.c
│   │   ├── __init__.py
│   │   ├── __init__.pyc
│   │   ├── spi.c
│   │   ├── spi.pyx
│   │   └── spi.so
│   ├── gpio
│   │   ├── gpio.c
│   │   ├── gpio_lib.c
│   │   ├── gpio_lib.h
│   │   ├── __init__.py
│   │   └── __init__.pyc
│   ├── i2c
│   │   ├── i2c.c
│   │   ├── i2c_lib.c
│   │   ├── i2c_lib.h
│   │   ├── __init__.py
│   │   └── __init__.pyc
│   ├── __init__.py
│   ├── __init__.pyc
│   ├── spi
│   │   ├── __init__.py
│   │   ├── __init__.pyc
│   │   ├── spi.c
│   │   ├── spi_lib.c
│   │   └── spi_lib.h
│   └── utilities
│       └── color.h
├── README.txt
└── setup.py

My setup file is:

from distutils.core import setup
from distutils.core import Extension

from Cython.Build import cythonize
from Cython.Distutils import build_ext


module_gpio = Extension('pyA13SOM.gpio',
                        sources=['pyA13SOM/gpio/gpio_lib.c', 'pyA13SOM/gpio/gpio.c'])

module_i2c = Extension('pyA13SOM.i2c',
                       sources=['pyA13SOM/i2c/i2c_lib.c', 'pyA13SOM/i2c/i2c.c'])

module_spi = Extension('pyA13SOM.spi',
                       define_macros=[('CYTHON_IN_USE', '1')],
                       sources=['pyA13SOM/spi/spi_lib.c', 'pyA13SOM/spi/spi.c'])

setup(
    name='pyA13SOM',
    version='0.2.0',
    packages=['pyA13SOM'],
    # ext_modules=[module_gpio, module_i2c, module_spi],
    cmdclass={'build_ext': build_ext},
    ext_modules=cythonize("pyA13SOM/cython/*.pyx"),

)

The tree is in ~/mydir/ . I go to ~/mydir/ and do: python setup.py install .

Everything in the build process is OK. Next I try to test import . When I import pyA13SOM.cython.spi , it should give me "Hello world" message. And it does.

~/mydir/$ **python -c "import pyA13SOM.cython.spi"**
Test:
Hellowwwwwwwwwww!

But when I do this from another directory:

~/someotherdir/$ **python -c "import pyA13SOM.cython.spi"**
ImportError: No module named cython.spi

Any idea why does this happen?

Answer 1

You might need to include the directory in which your newly built .spi file is located into your $PYTHONPATH. Otherwise python cannot find the file to import it. While you are in ~/mydir/, python searches the local path if I am not mistaken...

Depending on the shell you are using, you can include the ~/mydir/ directory into the pythonpath with the following:

for the bash and sh shells:

PYTHONPATH=$PYTHONPATH:~/mydir/
export $PYTHONPATH

for the csh/tcsh environment:

set PYTHONPATH = ($PYTHONPATH ~/mydir/)

These two commands add the ~/mydir/ temporarily to your $PYTHONPATH. If you want to add the path permanently, you will have to add the above commands to your ~/.bashrc or ~/.tcshrc, respectively.

Hope this helps...