conservative check for known exceptions in subprocess stderr.

[AdamGold]

Thank you for contributing to Pipenv!

The issue

#2553

The fix

Conservative checks of known exceptions when subprocess returns output.

The checklist

• Associated issue
• A news fragment in the news/ directory to describe this fix with the extension .bugfix, .feature, .behavior, .doc. .vendor. or .trivial (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.

[AdamGold]

This is a UX improvement PR. Do you guys think there is a better way of doing it?

[techalchemy]

hey, sorry for the delay -- made some suggestions for how to generalize this improvement a bit more -- thanks a ton for putting in the effort on this as it's really a big help and not likely something we will ever do otherwise

[techalchemy]

Won't known_exceptions_partition[1] and known_exceptions_partition[2] just be PermissionError: <message> in this case? I like where this is headed but I feel like it might belong in exceptions.py. Also note that it really isn't appropriate to manipulate c.err -- it is the stored stderr stream output from a subprocess that has already or is currently executing. We really should only ever manipulate how we interpret and display the result.

Possibly we should have some helper method like this:

KNOWN_EXCEPTIONS = {
    "PermissionError": "Permission denied:"
}

def prettify_exc(exc):
    matched_exceptions = [k for k in KNOWN_EXCEPTIONS.keys() if k in exc]
    errors = []
    for match in matched_exceptions:
        exc, exc_name, error = exc.rpartition(KNOWN_EXCEPTIONS[match])
        errors.append("{0} {1}".format(exc_name, crayons.red(decode_for_output(error))))
    else:
        errors.append("{0}".format(decode_for_output(exc)))
    return "\n".join(errors)

And then the exceptions themselves can share a dictionary of known exceptions and use prettify_exc when environments.is_verbose() is False

[AdamGold]

That's a good idea. I have pushed the prettify_exc implementation.

[techalchemy]

Sorry for being incredibly slow on this, but this is looking pretty good to me... I am excited to get things refactored in this direction.

Thanks for taking care of this!

[AdamGold]

@techalchemy, Awesome. Rebased to master.