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: /home/murilo/ros2_tutorial_workspace/src
   package format: 3
   version: 0.0.0
   description: TODO: Package description
   maintainer: ['murilo <murilomarinho@ieee.org>']
   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 identitifers:
   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
   
The sample Node
---------------

Given that it was created from a template, the file :file:`python_package_that_uses_the_library/python_package_that_uses_the_library/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] [1683598288.149167944] [node_that_uses_the_library]: sample_function_for_square_of_sum(0.19395834493833486,1.3891603395040568) returned 2.506264769030609.
   [INFO] [1683598288.149643378] [node_that_uses_the_library]: sample_class_with_random_name.get_name() returned qyOXLBEtzZ.
   [INFO] [1683598288.616095880] [node_that_uses_the_library]: sample_function_for_square_of_sum(0.7387236329957096,1.7650481260672202) returned 6.2688730214810775.
   [INFO] [1683598288.616604769] [node_that_uses_the_library]: sample_class_with_random_name.get_name() returned LCFNFyzwhk.
   [INFO] [1683598289.116050219] [node_that_uses_the_library]: sample_function_for_square_of_sum(0.003813494022560704,1.7056916575839387) returned 2.9224078633691604.
   [INFO] [1683598289.116553899] [node_that_uses_the_library]: sample_class_with_random_name.get_name() returned wrtTlOdanZ.