"No matching distribution found" is confusing when unsupported bzip2 package is actually available

[wsanchez]

• Pip version: 9.0.1
• Python version: 3.6.2
• Operating system: Ubuntu

I ran pip install Twisted and got this error message:

  Could not find a version that satisfies the requirement Twisted (from versions: )
Cleaning up...
No matching distribution found for Twisted

@dstufft figured out that my problem is that I built I python without bzip support. The error message above should say "I found Twisted, but you and your lame-ass Python can't have it because no bzip" (feel free to rephrase that) instead of telling me that there's no Twisted to be had, which is kinda confusing.

[pradyunsg]

On the other hand, would it make sense to print a warning when pip detects that there's a Python installation without bzip2? It is a fairly important stdlib component for pip, it's absence means pip lacks a fair amount of functionality so it would make sense that it gets at least a warning.

[xavfernandez]

If you had run pip with --verbose option you could have spotted:
https://github.com/pypa/pip/blob/9.0.1/pip/utils/__init__.py#L63
or
https://github.com/pypa/pip/blob/9.0.1/pip/index.py#L618

[wsanchez]

Sure, but there's an error being printed, and the error could do a better job of explaining what the problem-to-fix is. The current error looks like PyPI is missing the module being requested.

[chrahunt]

I think that adding a specific error message for bzip2, or any other specific reason for exclusion, would get complicated quickly. This is especially true if there are multiple packages excluded for different reasons. Maybe we could get a lot of benefit from an output like:

Some packages may have been found and excluded. To see details, re-run pip with --verbose.

If we actually want to commit to showing this only when at least one package has been found and excluded for some reason, then it could be

Some packages were found but excluded. To see details, re-run pip with --verbose.