pip team said they won't support setting limit for major version
of package being installed in the way below until it is supported
by PEP 440.

    pip install patch==1.x

The current way ==1.* conflicts with system shell expansion
and the other way is not known / not intuitive.

https://github.com/pypa/pip/issues/2737#issuecomment-97621684
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anatoly t.