"beza1e1" <[EMAIL PROTECTED]> wrote:
> I have such a statement as string: "distance = x**2 + y**2"
> x and y are undefined, so it is no executable Python code, but it is
> parseable. Now i'd like traverse through the AST and change Name('x')
> for the value i have elsewhere. And finally let Python resolve the
> computation.
you can use the parser class for this purpose:
http://www.effbot.org/librarybook/parser.htm
instead of manipulating the parse tree, you can use the AST to identify
the variables, create a dictionary with the current values, and use exec
or eval to evaluate it.
or you can use a regular expression to dig out all variable names.
or you can compile the expression and analyze the code object to find
the variable names, and use the dictionary/exec approach:
>>> expr = compile("distance = x**2 + y**2", "", "exec")
>>> expr.co_varnames
('distance',)
>>> list(set(expr.co_names) - set(expr.co_varnames))
['y', 'x']
>>> context = {"x": 10, "y": 20}
>>> exec expr in context
>>> context["distance"]
500
(the regular expression approach is probably the only one that's
guaranteed to work on all python implementations)
</F>
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