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Class LockType always seems to be returning None if waitflag is not
specified.
If you look up the documentation for the non dummy lock in lib ref
15.3.1 , none of the possible
results should be ‘None’, in fact it would always return True, except
when non-block is specified
And another thread is already holding the lock then it would return False
From the docs on acquire():
Acquire a lock, blocking or non-blocking. 
When invoked without arguments, block until the lock is unlocked, then
set it to locked, and return true. 
When invoked with the blocking argument set to true, do the same thing
as when called without arguments, and return true. 
When invoked with the blocking argument set to false, do not block. If a
call without an argument would block, return false immediately;
otherwise, do the same thing as when called without arguments, and
return true.

Seems like inconsistency to me, this simple patch should fix it.

r64903-64905 have the fixes for trunk, 3.0, and 2.5, respectively.
Thanks for reporting this, Henk. Andrii, I never even looked at your
patch since while I was evaluating the bug the problem was rather
obvious and simple, as you said. =) Thanks for the work, though.