Failing gracefully when installed Python is too old?

[Grant Edwards]

I can't figure out a way for a Python program to fail
gracefully if somebody attempts to run it with a version of
Python that's too old.

Checking sys.hexversion at runtime won't work because the
program might not even parse.  For example, attempting to run
a program containing list comprehensions under 1.5.2.

Is there any way to check the version at compile time?

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