Using a Python Library from another package (for :program:`ament_python`) ====================================================================== Let us create a package with a Node that uses the library we created in the prior example. Note that we must add the :code:`python_package_with_a_library` as a dependency to our new package. The easiest way to do so is through :program:`ros2 pkg create`. We also add :code:`rclpy` as a dependency so that our Node can do something useful. .. code :: console cd ~/ros2_tutorial_workspace/src ros2 pkg create python_package_that_uses_the_library \ --dependencies rclpy python_package_with_a_library \ --build-type ament_python \ --node-name node_that_uses_the_library resulting in yet another version of our favorite wall of text .. code-block:: console :emphasize-lines: 10 going to create a new package package name: python_package_that_uses_the_library destination directory: /root/ros2_tutorial_workspace/src package format: 3 version: 0.0.0 description: TODO: Package description maintainer: ['root '] licenses: ['TODO: License declaration'] build type: ament_python dependencies: ['rclpy', 'python_package_with_a_library'] node_name: node_that_uses_the_library creating folder ./python_package_that_uses_the_library creating ./python_package_that_uses_the_library/package.xml creating source folder creating folder ./python_package_that_uses_the_library/python_package_that_uses_the_library creating ./python_package_that_uses_the_library/setup.py creating ./python_package_that_uses_the_library/setup.cfg creating folder ./python_package_that_uses_the_library/resource creating ./python_package_that_uses_the_library/resource/python_package_that_uses_the_library creating ./python_package_that_uses_the_library/python_package_that_uses_the_library/__init__.py creating folder ./python_package_that_uses_the_library/test creating ./python_package_that_uses_the_library/test/test_copyright.py creating ./python_package_that_uses_the_library/test/test_flake8.py creating ./python_package_that_uses_the_library/test/test_pep257.py creating ./python_package_that_uses_the_library/python_package_that_uses_the_library/node_that_uses_the_library.py [WARNING]: Unknown license 'TODO: License declaration'. This has been set in the package.xml, but no LICENSE file has been created. It is recommended to use one of the ament license identifiers: Apache-2.0 BSL-1.0 BSD-2.0 BSD-2-Clause BSD-3-Clause GPL-3.0-only LGPL-3.0-only MIT MIT-0 Package structure ----------------- We'll be working on the following file structure. .. code-block:: console :emphasize-lines: 5 python_package_that_uses_the_library/ |-- package.xml |-- python_package_that_uses_the_library | |-- __init__.py | `-- node_that_uses_the_library.py |-- resource | `-- python_package_that_uses_the_library |-- setup.cfg |-- setup.py `-- test |-- test_copyright.py |-- test_flake8.py `-- test_pep257.py The sample Node --------------- Given that it was created from a template, the file :file:`node_that_uses_the_library.py` is currently *mostly* empty. Let us replace its contents with :download:`node_that_uses_the_library.py <../../ros2_tutorial_workspace/src/python_package_that_uses_the_library/python_package_that_uses_the_library/node_that_uses_the_library.py>` .. literalinclude:: ../../ros2_tutorial_workspace/src/python_package_that_uses_the_library/python_package_that_uses_the_library/node_that_uses_the_library.py :language: python :linenos: :lines: 24- Indeed, the most difficult part is to make and configure the library itself. After that, to use it in another package, it is straightforward. We :code:`import` the library. .. literalinclude:: ../../ros2_tutorial_workspace/src/python_package_that_uses_the_library/python_package_that_uses_the_library/node_that_uses_the_library.py :language: python :lines: 24-29 :emphasize-lines: 6 And then use the symbols we imported as we would with any other Python library. .. literalinclude:: ../../ros2_tutorial_workspace/src/python_package_that_uses_the_library/python_package_that_uses_the_library/node_that_uses_the_library.py :language: python :lines: 40-55 :emphasize-lines: 10, 14 Build and source ---------------- As always, this is needed so that our new package and node can be recognized by :program:`ros2 run`. .. include:: the_canonical_build_command.rst Run --- .. hint:: Remember that you can stop the node at any time with :kbd:`CTRL+C`. .. code :: console ros2 run python_package_that_uses_the_library node_that_uses_the_library Which outputs something similar to the shown below, but with different numbers and strings as they are randomized. .. code :: console [INFO] [1753585839.509922172] [node_that_uses_the_library]: sample_function_for_square_of_sum(0.9787232004970391,1.7320908702316369) returned 7.348512926060575. [INFO] [1753585839.510400755] [node_that_uses_the_library]: sample_class_with_random_name.get_name() returned GQkUZgSkje. [INFO] [1753585839.993999505] [node_that_uses_the_library]: sample_function_for_square_of_sum(0.7637556876478347,1.0377535114838756) returned 3.2454353945561767. [INFO] [1753585839.994351922] [node_that_uses_the_library]: sample_class_with_random_name.get_name() returned EztAWYuFMB. [INFO] [1753585840.494895006] [node_that_uses_the_library]: sample_function_for_square_of_sum(0.26638758438777976,1.1809445792770386) returned 2.0947703919786846. [INFO] [1753585840.495950422] [node_that_uses_the_library]: sample_class_with_random_name.get_name() returned ITLIHPOMgv. [INFO] [1753585840.994468589] [node_that_uses_the_library]: sample_function_for_square_of_sum(0.5244531764161572,1.7524376840394509) returned 5.184231990426279. [INFO] [1753585840.994695797] [node_that_uses_the_library]: sample_class_with_random_name.get_name() returned LGtybBngKv.