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Re: while True or while 1

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  Re: while True or while 1 Matteo Landi <matteo@matteolandi.net> - 2012-01-21 16:24 +0100

#19192 — Re: while True or while 1

Probably because of the fact it is possible to set True equal to False and
consequently then invalidate loop logic as presented below:

    True = False
    while True:
        ...

On the other hand `1' will always be evaluated as a constant.

Don't know, just guessing.


Matteo

On Jan/21, Andrea Crotti wrote:
> I see sometimes in other people code "while 1" instead of "while True".
> I think using True is more pythonic, but I wanted to check if there is
> any difference in practice.
> 
> So I tried to do the following, and the result is surprising.  For what
> I can see it looks like the interpreter can optimize away the 1 boolean
> conversion while it doesn't with the True, the opposite of what I
> supposed.
> 
> Anyone can explain me why is that, or maybe is my conclusion wrong?
> 
>   def f1():
>       while 1:
>           pass
> 
>   def f2():
>       while True:
>           pass
> 
>   In [10]: dis.dis(f)
>   2           0 SETUP_LOOP               3 (to 6)
> 
>   3 >>    3 JUMP_ABSOLUTE            3
> >>    6 LOAD_CONST               0 (None)
>               9 RETURN_VALUE
> 
>   In [9]: dis.dis(f1)
>   2           0 SETUP_LOOP              10 (to 13)
> >>    3 LOAD_GLOBAL              0 (True)
>               6 POP_JUMP_IF_FALSE       12
> 
>   3           9 JUMP_ABSOLUTE            3
> >>   12 POP_BLOCK
> >>   13 LOAD_CONST               0 (None)
>              16 RETURN_VALUE
> 
> -- 
> http://mail.python.org/mailman/listinfo/python-list
> 

-- 
http://www.matteolandi.net

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