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Forgive my directness, but the last post doesn't show the slightest 
clue about how Python works.  The existing test for a negative 
shift count takes place downstream from the interpreter in the 
int_lshift function in intobject.c (and the same for longobject.c).  
The RFE is to replace the line that raises a Value Error exception 
with a line that does something useful like flipping the sign of the 
argument and delegating to int_rshift.  That is a zero net change 
in code complexity.  The runtime of non-negative cases is 
likewise unchanged.  Is there someone else reading this who has 
an informed opinion?