[Python-Dev] variable name resolution in exec is incorrect (original) (raw)

Greg Ewing greg.ewing at canterbury.ac.nz
Thu May 27 05:13:16 CEST 2010

On 27/05/10 11:33, Michael Foord wrote:

On 27/05/2010 00:38, Greg Ewing wrote:

Maybe the second scope argument to exec() should be deprecated?

Sounds good to me, certainly ends the confusion over this undoubtedly unintuitive behaviour. :-)

Although it's a fair point that it can be useful to have a way of capturing definitions made by the execed code, while still making an environment of other stuff available to it.

So, I'd be in favour of changing the behaviour of exec so that the local scope is made visible inside functions. However, it would be non-trivial to implement this the way things are currently structured, which is probably one of the reasons it hasn't already been done.

I don't think that simply using LOAD_NAME inside the function would work, because that would only look in the function's own local namespace first, then in the global one. There is just no mechanism available at the moment for the function to know about the local namespace passed in to exec.

The way that functions get access to names in enclosing local scopes is by having them passed in as cells, but that mechanism is only available for optimised local namespaces, not ones implemented as dicts.

-- Greg

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