[issue21911] "IndexError: tuple index out of range" should include the requested index and tuple length

[Josh Rosenberg]

Josh Rosenberg added the comment:

Looking at a single lookup performed over and over isn't going to get you a very good benchmark. If your keys are constantly reused, most of the losses won't show themselves. A more fair comparison I've used before is the difference between using the bytes object produced by bytes.maketrans as the mapping object for str.translate vs. using the dictionary produced by str.maketrans. That gets you the dynamically generated lookups that don't hit the dict optimizations for repeatedly looking up the same key, don't predictably access the same memory that never leaves the CPU cache, etc.

Check the timing data I submitted with #21118; the exact same translation applied to the same input strings, with the only difference being whether the table is bytes or dict, takes nearly twice as long using a dict as it does using a bytes object. And the bytes object isn't actually being used efficiently here; str.translate isn't optimized for the buffer protocol or anything, so it's constantly retrieving the cached small ints; a tuple might be even faster by avoiding that minor additional cost.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21911>
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