Question about name scope
Ethan Furman
ethan at stoneleaf.us
Wed Feb 1 17:24:28 EST 2012
Ian Kelly wrote:
> I am not a dev, but I believe it works because assigning to locals()
> and assigning via exec are not the same thing. The problem with
> assigning to locals() is that you're fundamentally just setting a
> value in a dictionary, and even though it happens to be the locals
> dict for the stack frame, Python can't figure out that it should go
> and update the value of the optimized local to match. exec, on the
> other hand, compiles and executes an actual STORE_NAME operation. Of
> course, if the particular local variable hasn't been optimized by the
> compiler, then updating locals() works just fine (although you
> probably should not rely on this):
>
>>>> def f(x, y):
> ... locals()[x] = y
> ... print locals()[x]
> ... exec 'print ' + x
> ...
>>>> f('a', 42)
> 42
> 42
Definitely should rely on it, because in CPython 3 exec does not
un-optimize the function and assigning to locals() will not actually
change the functions variables.
~Ethan~
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