On 6/20/07, Christian Heimes <[EMAIL PROTECTED]> wrote: > Nick Coghlan wrote: > > Because (str(x) for x in seq) is not an improvement over map(str, x) - > > applying a single existing function to a sequence is a very common > > operation. > > > > map() accepts any function (given an appropriate number of sequences), > > and thus has wide applicability. > > > > filter() accepts any single argument predicate function (using bool() by > > default), and thus also has wide applicability. > > But map() and filter() can be easily replaced with a generator or list > comprehensive expression. [str(x) for x in seq] and [x for x in seq if > func(x)] are consider easier to read these days. > > IIRC map and filter are a bit slower than list comprehensive and may use > much more memory than a generator expression since map and filter are > returning a list of results.
No, in 3.0 they'll return iterables -- you really SHOULD read Guido's blog entry referred to at the top of this thread, <http://www.artima.com/weblogs/viewpost.jsp?thread=208549>, before discussing Python 3.0 issues. So, there's no reason their performance should suffer, either -- using today's itertools.imap as a stand-in for 3.0's map, for example: $ python -mtimeit -s'import itertools as it' -s'L=range(-7,17)' 'for x in it.imap(abs,L): pass' 100000 loops, best of 3: 3 usec per loop $ python -mtimeit -s'import itertools as it' -s'L=range(-7,17)' 'for x in (abs(y) for y in L): pass' 100000 loops, best of 3: 4.47 usec per loop (imap is faster in this case because the built-in name 'abs' is looked up only once -- in the genexp, it's looked up each time, sigh -- possibly the biggest "we should REALLY tweak the language to let this be optimized sensibly" gotcha in Python, IMHO). Alex _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
