Getting namespaces right when parsing/executing Python ASTs

Gordon Fraser gfraser79 at gmail.com
Tue Oct 7 16:55:03 CEST 2008


Hi,

Am Dienstag, den 07.10.2008, 15:30 +0100 schrieb Orestis Markou:
> Have you tried passing in empty dicts for globals and locals? I think
> that the defaults will be the *current* globals and locals, and then
> of course your namespace is broken...

That seems to work, thanks. Still trying to make sense of the manual for
eval, as it says if the passed globals dict lacks '__builtins__' it will
copy the current globals, and if no dict is passed it will use the
current globals (so what's the difference?). But anyway, as long as it
works I'm happy!

Thanks,
Gordon


> 
> On Tue, Oct 7, 2008 at 1:26 PM, Gordon Fraser <gfraser79 at gmail.com> wrote:
> > Hi,
> >
> > I'm trying to parse Python code to an AST, apply some changes to the AST
> > and then compile and run the AST, but I'm running into problems when
> > trying to evaluate/execute the resulting code object. It seems that the
> > global namespace differs depending on where I call parse and eval/exec.
> >
> > The following code parses a file, compiles and then evaluates the AST.
> > If I call Python directly on this code, then it works:
> >
> >        import sys, parser
> >        ast = parser.suite(open(sys.argv[1]).read())
> >        code = ast.compile()
> >        exec(code)
> >
> > ...and it also works this way with Python2.6:
> >
> >    ast = compile(open(sys.argv[1]).read(), "<AST>",
> > 'exec',_ast.PyCF_ONLY_AST)
> >    code = compile(ast, "<AST", "exec")
> >    exec(code)
> >
> > However, if I include that snippet in a different scope (some function
> > or class), then the namespace that the code object will have differs -
> > it seems the symbols defined in the AST are not included when executing
> > the code. For example:
> >
> >        import sys,parser
> >
> >        def main():
> >            ast = parser.suite(open(sys.argv[1]).read())
> >            code = ast.compile()
> >            exec(code)
> >
> >        if __name__ == "__main__":
> >          main()
> >
> > In particular this is a problem if I'm parsing a module with several
> > functions - none of these functions actually ends up in the scope of the
> > code object (same behavior with Python2.6 and the PyCF_ONLY_AST
> > version).
> >
> > The function "exec" takes parameters for globals and locals, but I have
> > no idea where to get these dictionaries from the "parser" module. My
> > guess is that I am misunderstanding something about how Python treats
> > namespaces. Can anyone help me here?
> >
> > Thanks,
> > Gordon
> >
> >
> > --
> > http://mail.python.org/mailman/listinfo/python-list
> >
> 
> 
> 




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