"Tail recursion" in callbacks

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When some code that is itself a callback (e.g. a fd handler) wants to call some 
other code (maybe a protocol method) immediately before returning, I used to 
use call_soon() to delay the other call.  I think this just causes more work 
going through the event loop.  I think it's safe to make such calls directly, 
provided that

1. It is the last call before returning

2. There is no try/execpt or try/finally surrounding it

Original issue reported on code.google.com by gvanrossum@gmail.com on 20 Mar 2013 at 8:32