[Python-Dev] PEP 289 - Generator Expressions (original) (raw)

[Python-Dev] PEP 289 - Generator Expressions - Let's Move Forward

Samuele Pedroni pedronis at bluewin.ch
Mon May 3 09:47:08 EDT 2004

At 21:08 02.05.2004 -0700, Guido van Rossum wrote:

> Armin Rigo <arigo at tunes.org>: > > > Early binding is closer to the idea that turning a listcomp into a > > genexprs should just work if you only iterate once on the result.

Greg Ewing: > I'm not sure that's an idea we should be promulgating in the first > place. The original motivation for generator expressions was things > like > > total = sum(x**2 for x in stuff) > > where not only will the sequence be used just once, but it will be > used immediately before doing anything else. >

yes, but the question is how much easy is to grasp what "used immediately" means for a genexp, or IOW how much education is needed.

this looks innocent enough:

l = list_of_my_strings() for pfx in discard_prefixes: l = ( x for x in l if not x.startswith(pfx) ) # this is not using l immediately use_strings(l)

> Those are the use cases we need to advertise this as targeting, I > think, not "any listcomp that's only used once".

Right -- thanks for saying it so clearly! Early binding seems to be trying to solve a problem with a use for genexprs that's questionable at best.

More information about the Python-Dev mailing list