Print cache location is --cache-dir is given no value ?

[Carreau]

• Pip version: 9.0.1-15-g47169621
• Python version: 3.5
• Operating System:OS X

I needed to purge pip-cache, and mechanically expected pip --cache-dir to print the location.

Though about that ?

The alternative would be to add a --purge-cache or similar.

I expect the first one would be easier, and less controversial.

[dstufft]

I would prefer not to directly expose the cache dir location, however adding a mechanism to purge the cache is reasonable. That is a duplicate of #2819.