vext makes builds with "python3 -m build" fail in environments without module "colorama"

[nathanael-naeri]

Hi, I'm building distribution packages for a project at work with the PEP 517 compliant builder build, using the command line python3 -m build. PEP 517 builders are now recommended over using setuptools as in the past (python3 setup.py sdist|bdist_wheel), if I understand correctly.

In a virtual environment with vext, the build fails with the error ImportError: No module named colorama and the following traceback:

(.dev) $ python3 -m build
Traceback (most recent call last):
  File "/usr/lib/python3.8/runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.8/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/home/me/.dev/lib/python3.8/site-packages/build/__main__.py", line 390, in <module>
    main(sys.argv[1:], 'python -m build')
  File "/home/me/.dev/lib/python3.8/site-packages/build/__main__.py", line 337, in main
    _setup_cli()
  File "/home/me/.dev/lib/python3.8/site-packages/build/__main__.py", line 67, in _setup_cli
    import colorama
  File "/home/me/.dev/lib/python3.8/site-packages/vext/gatekeeper/__init__.py", line 204, in load_module
    raise ImportError("No module named %s" % modulename)
ImportError: No module named colorama

This is because build imports colorama, an optional dependency which is not present in the virtual environment, in a try-catch block where the expected exception is of class ModuleNotFoundError, a subclass of ImportError: see import statement here. However, vext raises an ImportError when it does not find the missing module, so this exception is not caught: see here.

I believe ModuleNotFoundError should be raised instead (since Python 3.6).

Alternatively, one could (should?) disable vext with vext --disable before building distribution packages.