Missing dependencies on 'six' and 'numpy'

[jhaiduce]

sphinx_fortran uses the packages 'six' and 'numpy' but they are not automatically installed by pip when sphinx-fortran is installed. Attempting to use sphinx_fortran without first manually installing 'six' produces the following error:

Extension error:
Could not import extension sphinxfortran.fortran_domain (exception: No module named 'six')

Similarly, if numpy is missing:

Extension error:
Could not import extension sphinxfortran.fortran_autodoc (exception: No module named 'numpy')

[tuoping]

I already installed six and numpy. And "import sphinxfortran.fortran_domain" works fine in python command line interface. But this Error still occurs when I put

extensions = ['sphinxfortran.fortran_domain']

in conf.py.

[Guymer]

I have come across this using the "Read The Docs" platform, as it is a very lightweight installation. I have to put "numpy" and "six" in a "requirements.txt" file and link it in using a ".readthedocs.yaml" configuration file, only then does Sphinx not complain about it.