Software Engineering: Python Modules

How to create reusable Python modules

The src folder of a ROS package should contain both Python and C++ code. C++ code goes directly in src, while Python code goes in src/<package_name>. This is because <package_name> will be the name of the Python module.

Say you want pr2_pick_manipulation to be a module that people can reuse in other packages.

• mkdir -p pr2_pick_manipulation/src/pr2_pick_manipulation
• vim pr2_pick_manipulation/src/pr2_pick_manipulation/grasp_generation.py
• vim pr2_pick_manipulation/src/pr2_pick_manipulation/__init__.py
  • Inside __init__.py, import names inside the pr2_pick_manipulation folder like from .grasp_generation import GraspGenerator
• Create a setup.py in the root of the package directory:

from distutils.core import setup
from catkin_pkg.python_setup import generate_distutils_setup

# fetch values from package.xml
setup_args = generate_distutils_setup(
    packages=['pr2_pick_manipulation'],
    package_dir={'': 'src'})

setup(**setup_args)

• Uncomment catkin_python_setup() in the CMakeLists.txt

Now, outside of the package, you can depend on pr2_pick_manipulation the same way you depend on any other package. You should be able to import code from your module like so:

from pr2_pick_manipulation import GraspingStrategy