Using flatpak-pip-generator resulting in "ERROR: could not find a version" when compiling

Question

The full log can be seen below. I am using flatpak-pip-generator with requirements.txt. Without using the requirements file I get the same error. (I get the error at compiling the project)

  ERROR: Command errored out with exit status 1:
   command: /usr/bin/python3 /usr/lib/python3.8/site-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-myezehl4/overlay --no-warn-script-location --no-binary :none: --only-binary :none: --no-index --find-links file:///run/build/python3-numpy -- 'setuptools<49.2.0' wheel 'Cython>=0.29.21'
       cwd: None
  Complete output (3 lines):
  Looking in links: file:///run/build/python3-numpy
  ERROR: Could not find a version that satisfies the requirement setuptools<49.2.0 (from versions: none)
  ERROR: No matching distribution found for setuptools<49.2.0
  ----------------------------------------
ERROR: Command errored out with exit status 1: /usr/bin/python3 /usr/lib/python3.8/site-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-myezehl4/overlay --no-warn-script-location --no-binary :none: --only-binary :none: --no-index --find-links file:///run/build/python3-numpy -- 'setuptools<49.2.0' wheel 'Cython>=0.29.21' Check the logs for full command output.

Answer 1

I have solved my problem by locking specific versions of my python dependencies (strangely how it only worked for me this way if I use flatpak-pip-generator). I have also used cppy because apparently matplotlib depends on that, although it seems that is not explicitly declared in the dependencies wheel. My requirements.txt file is now:

numpy==1.17.3
# matplotlib implicitly requires cppy
cppy==1.1.0
matplotlib==3.1.1
sympy==1.6.2