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From: Peter Otten <__peter__@web.de>
Subject: Re: [Q] How to exec code object with local variables specified?
Date: Thu, 20 Sep 2012 15:15:24 +0200
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Xref: csiph.com comp.lang.python:29550

Makoto Kuwata wrote:

> Is it possible to run code object with local variables specified?
> I'm trying the following code but not work:
> 
>     def fn():
>        x = 1
>        y = 2
>     localvars = {'x': 0}
>     exec(fn.func_code, globals(), localvars)
>     print(localvars)
>     ## what I expected is: {'x': 1, 'y': 2}
>     ## but actual is:      {'x': 0}
> 
> Python: 2.7.3

>>> loc = {}
>>> exec("x = 1; y = 2", globals(), loc)
>>> loc
{'y': 2, 'x': 1}

However, this won't work with the code object taken from a function which 
uses a different a bytecode (STORE_FAST instead of STORE_NAME):


>>> import dis
>>> def f(): x = 1
... 
>>> dis.dis(f)
  1           0 LOAD_CONST               1 (1)
              3 STORE_FAST               0 (x)
              6 LOAD_CONST               0 (None)
              9 RETURN_VALUE        
>>> dis.dis(compile("x=1", "<nofile>", "exec"))
  1           0 LOAD_CONST               0 (1)
              3 STORE_NAME               0 (x)
              6 LOAD_CONST               1 (None)
              9 RETURN_VALUE