On Wed, Oct 23, 2019 at 10:59 AM Steven D'Aprano <st...@pearwood.info> wrote: > > For the example you gave, besides saving a few characters I don't see the > > advantage over the existing way we have to do that: > > > > 'one two three'.split() > > One of the reasons why Python is "slow" is that lots of things that can > be done at compile-time are deferred to run-time. I doubt that splitting > short strings will often be a bottle-neck, but idioms like this cannot > help to contribute (even if only a little bit) to the extra work the > Python interpreter does at run-time: > > load a pre-allocated string constant > look up the "split" attribute in the instance (not found) > look up the "split" attribute in the class > call the descriptor protocol which returns a method > call the method > build and return a list > garbage collect the string constant > > versus: > > build and return a list from pre-allocated strings > > (Or something like this, I'm not really an expert on the Python > internals, I just pretend to know what I'm talking about.) >
This could be done as an optimization without changing syntax or semantics.. As long as the initial string is provided as a literal, it should be possible to call the method at compile time, since (as far as I know) every string method is a pure function. It's made a little more complicated by the problem of mutable return values (str.split() returns a list, and if you call it again, you have to get a new unique list in case one of them gets mutated), but if you immediately iterate over it, that won't be a problem. Currently, the CPython optimizer can recognize constructs like "if x in [1,2,3,4]" or "for x in [1,2,3,4]" and use a literal tuple instead of building a list. Recognizing the splitting of a string as another equivalent literal could be done the same way. Whether it's worthwhile or not is another question, but if the performance penalty of the run-time splitting is a problem, that CAN be fixed even without new syntax. ChrisA _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/WBGO662XIAWQ7UZF6D5LDNHZT7DLMB4B/ Code of Conduct: http://python.org/psf/codeofconduct/
