Add an optional --index-url argument similar to that in pip

[nmacinnis]

Adds an optional --index-url argument so that hashin can be used with an alternate package index.

Pip supports this behavior with the same argument. Hashin was hardcoded to point at pypi.org, so if you happened to be working with an alternate index, hashin couldn't help you.

Pip also accepts an --extra-index-url argument, but I'm guessing that hashin won't benefit much from supporting the same. I expect the main use case of --index-url to be a package or package version that only exists on the alternate index.

[peterbe]

If you accept my suggestion for using a constant then the string "https://pypi.org" only needs to appear exactly 1 single time. Both in the main file and in the unit test(s).

[peterbe]

It doesn't make sense to let this be None. It could be ..., index_url='https://pypi.org') but then you'd have to write that string twice. Once here and once in the argparse set-up stuff below.

I think I'd rather this simply be another mandatory positional argument.

[peterbe]

How about moving this to the top of the file. Something like this:

DEFAULT_INDEX_URL = os.environ.get('INDEX_URL', 'https://pypi.org')

and then, here, do...:

parser.add_argument(
        "--index-url",
        help="package index url (default {0})".format(DEFAULT_INDEX_URL),
        default=DEFAULT_INDEX_URL,

[nmacinnis]

@peterbe thanks for the feedback!

I was already looking at reducing the size of the changeset by defaulting the index url kwarg in a few places. I've incorporated the env var idea. Also made the index url kwarg into a regular positional argument in get_package_data because it is obviously mandatory as you noted.

[peterbe]

Love it!

I'll update the README when I make a release.