Web API installation fails with newer version of psutil

[bonjourmauko]

Hi there!

I really enjoy OpenFisca, but I recently encountered an issue.

Here is what I did:

I tried to install the Web API with the following command:

pip install 'OpenFisca-Core[web-api]' --upgrade --upgrade-strategy eager

Here is what I expected to happen:

For it to work correctly.

Here is what actually happened:

It failed to deploy the Web API due to a failed installation of psutil:

+ pip install 'OpenFisca-Core[web-api]' --upgrade --upgrade-strategy eager
Requirement already up-to-date: OpenFisca-Core[web-api] in /home/openfisca/virtualenvs/api-fr-latest/lib/python3.7/site-packages (34.4.5)
Collecting psutil<6.0.0,>=5.4.7 (from OpenFisca-Core[web-api])
  Using cached https://files.pythonhosted.org/packages/47/ea/d3b6d6fd0b4a6c12984df652525f394e68c8678d2b05075219144eb3a1cf/psutil-5.6.4.tar.gz
  Installing build dependencies ... error
  Complete output from command /home/openfisca/virtualenvs/api-fr-latest/bin/python3.7 /home/openfisca/virtualenvs/api-fr-latest/lib/python3.7/site-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-fbeynbnv/overlay --no-warn-script-location --no-binary :none: --only-binary :none: -i https://pypi.org/simple -- "setuptools >= 41.0.0" "wheel >= 0.29.0":
  Traceback (most recent call last):
    File "/home/openfisca/.pyenv/versions/3.7.0/lib/python3.7/runpy.py", line 193, in _run_module_as_main
      "__main__", mod_spec)
    File "/home/openfisca/.pyenv/versions/3.7.0/lib/python3.7/runpy.py", line 85, in _run_code
      exec(code, run_globals)
    File "/home/openfisca/virtualenvs/api-fr-latest/lib/python3.7/site-packages/pip/__main__.py", line 16, in <module>
      from pip._internal import main as _main  # isort:skip # noqa
    File "/home/openfisca/virtualenvs/api-fr-latest/lib/python3.7/site-packages/pip/_internal/__init__.py", line 4, in <module>
      import locale
    File "/home/openfisca/.pyenv/versions/3.7.0/lib/python3.7/locale.py", line 16, in <module>
      import re
    File "/home/openfisca/.pyenv/versions/3.7.0/lib/python3.7/re.py", line 143, in <module>
      class RegexFlag(enum.IntFlag):
  AttributeError: module 'enum' has no attribute 'IntFlag'
  
  ----------------------------------------
Command "/home/openfisca/virtualenvs/api-fr-latest/bin/python3.7 /home/openfisca/virtualenvs/api-fr-latest/lib/python3.7/site-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-fbeynbnv/overlay --no-warn-script-location --no-binary :none: --only-binary :none: -i https://pypi.org/simple -- "setuptools >= 41.0.0" "wheel >= 0.29.0"" failed with error code 1 in None
You are using pip version 19.0.3, however version 19.3.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

Here is data (or links to it) that can help you reproduce this issue:

https://pastebin.com/mRW1f4ej

Context

• For the source of the error see Fusion de la CMU-C et de l'ACS openfisca-france#1369 and Utilise le bon nom de variable dans la CSS openfisca-france#1381
• For a possible cause / solution see AttributeError: module 'enum' has no attribute 'IntFlag' iterative/dvc#1995

I identify more as a:

• Developer (I create tools that use the existing OpenFisca code).