Introduce version info as a tuple of int

[kitchoi]

ETS packages have __version__ as a string, e.g. "4.5.0". That is fine and is an expected format.

But sometimes we want to use the version information for things like skipping a test for a specific version range (e.g. enthought/pyface#656), then we have to resort to parsing the version string. It is not hard to do, but it would have been easier if a version_info or __version_info__ as a tuple of int is provided by the package already along with __version__.

e.g.

__version__ = "6.1.0"
__version_info__ = (6, 1, 0)

A similar topic was discussed a long time ago: enthought/distributed-array-protocol#16

[rahulporuri]

sounds like https://docs.python.org/3/library/sys.html#sys.version and https://docs.python.org/3/library/sys.html#sys.version_info. Additionally, __version_info__ can be a named tuple (major, minor, micro) instead of needing to index into the tuple to get information.

[rahulporuri]

Note that sys.version_info is a tuple of length 5 - where the last two elements represent releaselevel and serial. I'm not sure what serial refers to and I don't see much use for releaselevel at the moment.

[mdickinson]

We have had release-candidate releases of Traits - the releaselevel would be useful for that.

We'd also ideally want the dev stuff to go into the version_info somewhere, for development releases.

Having said that, version comparison becomes very messy if you want to include the releaselevel component, so we probably just stick to using the first 3 entries for version comparison. If we really need to do version comparison right reliably, covering all the various edge cases, the right way is to let pkg_resources or packaging handle it rather than try to do it ourselves.

[mdickinson]

I'd drop the serial part, though.

[mdickinson]

The other part of this is that where possible we should do direct tests for the thing we care about rather than using version numbers as a proxy. For example, prefer a try / except ImportError around a from traitsui.api import ThingThatMightNotBeThere, rather than a version check.