[Python-Dev] Auto-str and auto-unicode in join (original) (raw)

Nick Coghlan ncoghlan at iinet.net.au
Tue Aug 31 23:00:43 CEST 2004

M.-A. Lemburg wrote:

Tim Peters wrote:

If we were to do auto-str, it would be better to rewrite str.join() as a 1-pass algorithm, using the kind of "double allocated space as needed" gimmick unicode.join uses. It would be less efficient if auto-promotion to Unicode turns out to be required, but it's hard to measure how little I care about that; it might be faster if auto-str and Unicode promotion aren't needed (as only 1 pass would be needed). FWIW, I'm -1 on doing auto-conversion using str()/unicode() in .join().

I'm leaning that way myself. The 'auto-str' behaviour gives significant speed increases over the ''.join([str(x) for x in seq]) idiom, but the semantics become tricky when unicode, strings and things which are neither get mixed in the sequence. It also increases the complexity of the C code for the join methods.

(Note that the version of auto-str I tried out doesn't actually mimic the list comprehension idiom - it tries to detect unicode and switch join implementations as appropriate, etc, etc.)

Cheers, Nick.

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