How to declare an external python dependency in ros2

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Hello, I am trying to understand what is the proper way of declaring an external python dependency in ros2-foxy.

What I want to do is create a simple python only ros2 package, and add some dependency to a python module in it, in my case it is tinymovr, that should be installed from pip.

So I create the package following this tutorial.

ros2 pkg create --build-type ament_python --node-name example_node example_python

Edit the main of the generated example_node.py file to import the dependency:

import tinymovr
def main():
    print('Hi from example_python.')
if __name__ == '__main__':
    main()

Now build, source and run the package:

colcon build
source install/local_setup.sh
ros2 run example_python example_node

Since I didn't specify anywhere the dependency, I get a nice ModuleNotFoundError

 File "~/ros2_ws/install/example_python/lib/python3.8/site-packages/example_python/example_node.py", line 1, in <module>
    import tinymovr
ModuleNotFoundError: No module named 'tinymovr'

So now where should I do it?

My first try is to edit the setup.py file and edit the install_requires field:

 install_requires=['setuptools', 'tinymovr'],

But when I build and run, there is still the ModuleNotFoundError.

I read that colcon is meant only for building, and I should use rosdep to install external dependencies. And if I understand correctly I should add some <depend> tag in the package.xml file. On ubuntu it can install system packages via apt, using a package not already installed for example:

<depend>python3-mypy</depend>

When I run

rosdep install --from-paths src --ignore-src -r -y

It nicely proposes to install it:

Continuing to install resolvable dependencies...
executing command [sudo -H apt-get install -y python3-mypy]

However I don't understand how to tell rosdep to install a package via pip. Maybe it is not supposed to do this. But why doesn't colcon install stuff from the setup.py file? I also tried with the setup.cfg file with no success.

Thank you for reading, adding examples for this case or mentioning it in the tutorial would be great.