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Python from Wise Guy's Viewpoint

Frode Vatvedt Fjeld frodef at cs.uit.no
Tue Oct 21 11:13:30 EDT 2003 
Alex Martelli <aleax at aleax.it> writes:

> [..] the EXISTING call to foo() will NOT be "affected" by the "del
> foo" that happens right in the middle of it, since there is no
> further attempt to look up the name "foo" in the rest of that call's
> progress. [..]

What this and my other investigations amount to, is that in Python a
"name" is somewhat like a lisp symbol [1]. In particluar, it is an
object that has a pre-computed hash-key, which is why
hash-table/dictionary lookups are reasonably efficient. My worry was
that the actual string hash-key would have to be computed at every
function call, which I believe would slow down the process some 10-100
times. I'm happy to hear it is not so.

[1] One major difference being that Pyhon names are not first-class
    objects. This is a big mistake wrt. to supporting interactive
    programming in my personal opinion.

> As for your worries elsewhere expressed that name lookup may impose
> excessive overhead, in Python we like to MEASURE performance issues
> rather than just reason about them "abstractly"; which is why Python
> comes with a handy timeit.py script to time a code snippet
> accurately. [...]

Thank you for the detailed information. Still, I'm sure you will agree
that sometimes reasoning about things can provide insight with
predictive powers that you cannot achieve by mere experimentation.

-- 
Frode Vatvedt Fjeld
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