Tested a 2.0alpha00 release using test.pypi.org. It seems to be doing
the right thing as seen at https://test.pypi.org.

Using:

 pip download --index-url https://test.pypi.org/simple roundup

got 1.6.1 as expected.

 pip download --index-url https://test.pypi.org/simple 'roundup==2.0.0'
 pip download --index-url https://test.pypi.org/simple 'roundup==2.0'

errored which is fine as there is only an alpha release available

 pip download --index-url https://test.pypi.org/simple 'roundup==2.0a'
 pip download --index-url https://test.pypi.org/simple 'roundup>=2.0alpha'

downloaded the 2.0 alpha (roundup-2.0alpha00.tar.gz) release as desired.