[Python-porting] Strange behavior of eval() in Python 3.1

[Georg Brandl]

Am 29.08.2010 17:16, schrieb Bo Peng:
>> Note that this specific issue only appears because you're using eval().
>> For static code, your access to "a" outside of the comprehension's scope
>> will be recognized and a proper closure generated.
> 
> Thank you very much for your explanation and now I have a real problem
> to fix for my Python extension module. More specifically, I call
> "eval(expression, module_dict, user_dict)" to evaluate expressions in
> user_dict. However, to evaluate expressions such as "[a[x] for x in
> a]", I would need "eval(expression, user_dict, user_dict)" to make 'a'
> available in globals. But then I do not have access to names in
> module_dict, and simple expressions such as 'len(a)' would fail
> because I am doing all these from the C/C++ level and there is no
> __builtins__ in user_dict.

Surely you can do

namespace = module_dict.copy()
namespace.update(user_dict)
eval(..., namespace)

?

Georg

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