Critical sections and mutexes

[Skip Montanaro]

    dave> P.S. - Print statements are not atomic and do not fall in the same
    dave> realm as "normal" Python operations (e.g. "i = 5") ...

Assignment is not atomic either.  Your example would byte compile to

    LOAD_CONST 5
    STORE_FAST i

As others have mentioned, at the level of individual opcodes Python is
atomic.  The statement

    i = j

would have to be protected if j could be rebound or the object j referenced
could be modified by another thread.

-- 
Skip Montanaro (skip at pobox.com)
http://www.mojam.com/
http://www.musi-cal.com/