[Python-Dev] PEP for Better Control of Nested Lexical Scopes (original) (raw)

Terry Reedy tjreedy at udel.edu
Wed Feb 22 20:09:41 CET 2006

"Almann T. Goo" <almann.goo at gmail.com> wrote in message news:7e9b97090602212336ka0b5fd8r2c85b1c0e914aff1 at mail.gmail.com...

IMO, Having properly nested scopes in Python in a sense made having closures a natural idiom to the language and part of its "user interface." By not allowing the name re-binding it almost seems like that "user interface" has a rough edge that is almost too easy to get cut on.

I can see now how it would look that way to someone who has experience with fully functional nested scopes in other languages and who learns Python after no-write nested scoping was added. What is not mentioned in the ref manual and what I suppose may not be obvious even reading the PEP is that Python added nesting to solve two particular problems. First was the inability to write nested recursive functions without the hack of stuffing its name in the global namespace (or of patching the byte code). Second was the need to misuse the default arg mechanism in nested functions. What we have now pretty well fixes both.

Terry Jan Reedy

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