Re: andmap and ormap
Peter Otten wrote: > def andmap(predicate, items): > return False not in (predicate(item) for item in items) > > def ormap(predicate, items): > return True in (predicate(items) for item in items) These are both broken because they imply the test (in e. g. ormap) if True == predicate(item): ... where if predicate(item): ... would be appropriate. Sorry for the garbage post. Follow Felipe's or Scott's recipes. Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
[EMAIL PROTECTED] wrote: > The following works perfectly: > import operator > def andmap(b,L): > return reduce(operator.and_, [b(x) for x in L]) > def ormap(b,L): > return reduce(operator.or_, [b(x) for x in L]) Note your [b(x) for x in L] evaluates b(x) for all elements of L before you begin the analysis. In 2.3 and beyond, you could define: def imap(function, source): for element in source: yield function(element) And apply any or all (as defined below) to imap(b, L) Although, you often needn't use bool(expr) in Python, more things are reasonable to use directly as tests; if implicitly converts to bool. So, for those cases, you could simply use any(L) or all(L). If you wish to use any and all (coming in 2.5), you could go with: def any(iterable): '''True iff at least one element of the iterable is True''' for element in iterable: if element: return True # or element and change the definition return False def all(iterable): '''True iff no element of the iterable is True''' for element in iterable: if not element: return False return True These will short-circuit in 2.3 and up (where iterators live). In 2.4 and up, generator expressions can be used: any(x*7-4 > 100 for x in xrange(50)) Even in 2.3, any and all as defined above work with generators: def generates(limit): for i in xrange(limit): yield i * 7 - 4 > 100 any(generates(8)) True any(generates(8)) False --Scott David Daniels [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
"Joel Hedlund" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] >> footnote: if you have a recent Python 2.5 build, > > Who would have that? Is it a good idea to use a pre-alpha python version? The pre-public release version compiles as 'alpha0'. I have the impression the current alpha0 is being kept closer to releaseable more of the time than used to be the case. For instance, the developers recently set up a buildbot system to compile and run all unit tests on several systems with a variety of hardware and OSes up to several times a day. The results are available at http://www.python.org/dev/buildbot/ At of minutes ago, 5 systems are green (ok), 1 orange (warn) , and 1 red (fail). > ... Or should I start grabbing the Subversion trunk on a nightly basis? 'Should' if you want to experiment with new features or test existing code now rather than later. I would only grab it when the tests pass on the system closest to yours, and only repeat when there is a reason to. Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
The following works perfectly: import operator def andmap(b,L): return reduce(operator.and_, [b(x) for x in L]) def ormap(b,L): return reduce(operator.or_, [b(x) for x in L]) Thanks! -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
Peter Otten wrote: > def ormap(predicate, items): > return True in (predicate(items) for item in items) should be def ormap(predicate, items): return True in (predicate(item) for item in items) Hmmpf. Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
Peter Otten wrote: > Python 2.5 will feature similar functions any() and all() which seem to have > a fixed predicate == bool, though. You cannot write all(predicate, list) but all(predicate(x) for x in list) Georg -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
Joel Hedlund wrote: >> footnote: if you have a recent Python 2.5 build, > > Who would have that? Is it a good idea to use a pre-alpha python version? > Or any unrealeased python version for that matter? I was under the impression > that > the recommended way to go for meager developers in python like myself is to > stick > with the latest stable production release (2.4.2 at the time of writing I believe). > Or should I start grabbing the Subversion trunk on a nightly basis? As most of the new features 2.5 is going to have are already implemented, it's quite possible that people do checkout the SVN trunk and play with them. Course, Fredrik could have said "In 2.5 you'll be able to write..." Georg -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
[EMAIL PROTECTED] wrote: > def ormap(b,L): > if True in map(b,L): return True > else: return False > > Is this good enough? No, because - (as Felipe observed) it doesn't shortcut, i. e. it always evaluates b(item) for all items in L. - it creates a temporary list - if truthvalue: return True else: return False is redundant and just plain ugly Just write return truthvalue or, when truthvalue may consume a lot of memory, return bool(truthvalue) # or: return not not truthvalue Which gives: def andmap(predicate, items): return False not in (predicate(item) for item in items) def ormap(predicate, items): return True in (predicate(items) for item in items) > andmap((lambda t: boolean(t)),L) Superfluous lambda alert: make that andmap(boolean, L) Python 2.5 will feature similar functions any() and all() which seem to have a fixed predicate == bool, though. Peter -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
> footnote: if you have a recent Python 2.5 build, Who would have that? Is it a good idea to use a pre-alpha python version? Or any unrealeased python version for that matter? I was under the impression that the recommended way to go for meager developers in python like myself is to stick with the latest stable production release (2.4.2 at the time of writing I believe). Or should I start grabbing the Subversion trunk on a nightly basis? Cheers! /Joel Hedlund -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
Felipe Almeida Lessa wrote: > The problem is that it will evaluate all possibilities needlessly. Try > (not tested and 2.4-only): footnote: if you have a recent Python 2.5 build, you can make them even shorter: >>> help(any) any(...) any(iterable) -> bool Return True if bool(x) is True for any x in the iterable. >>> help(all) all(...) all(iterable) -> bool Return True if bool(x) is True for all values x in the iterable. -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
> Does python have andmap and ormap: > > andmap((lambda t: boolean(t)),L) > > gives True if boolean(t) is True for all t in L and False otherwise? > And > > ormap((lambda t: boolean(t)),L) > > gives True if boolean(t) is True for some t in L and False otherwise? > One can use a list comprehension like > > [x for x in L if not(False in map((lambda t: boolean(t)),L))] > > as an example of selection by andmap, and > > [x for x in L if (True in map((lambda t: boolean(t)),L))] > > as an example of selection by ormap. > > How does one define andmap/ormap so its first argument is a boolean > procedure or lambda? > > def andmap(b,L): > if False in map(b,L): return False > else: return True > > def ormap(b,L): > if True in map(b,L): return True > else: return False import operator reduce(operator.and_, [predcidate(o) for o in objects]) predicate can be a lambda, if it has to be. Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
On 14 Mar 2006 04:23:55 -0800, [EMAIL PROTECTED] wrote: > Hello, > Does python have andmap and ormap: > andmap((lambda t: boolean(t)),L) > gives True if boolean(t) is True for all t in L and False otherwise? > And > ormap((lambda t: boolean(t)),L) > gives True if boolean(t) is True for some t in L and False otherwise? import operator reduce( L, operator.and_ ) # andmap reduce( L, operator.or_ ) # ormap > One can use a list comprehension like [ ... ] > Is this good enough? If it works, and works correctly, then it's good enough. Regards, Dan -- Dan Sommers <http://www.tombstonezero.net/dan/> "I wish people would die in alphabetical order." -- My wife, the genealogist -- http://mail.python.org/mailman/listinfo/python-list
Re: andmap and ormap
Em Ter, 2006-03-14 às 04:23 -0800, [EMAIL PROTECTED] escreveu: > def andmap(b,L): > if False in map(b,L): return False > else: return True > > def ormap(b,L): > if True in map(b,L): return True > else: return False > > Is this good enough? The problem is that it will evaluate all possibilities needlessly. Try (not tested and 2.4-only): def andmap(func, objs): for boolean in (func(obj) for obj in objs): if not boolean: return False return True def ormap(func, objs): for boolean in (func(obj) for obj in objs): if boolean: return True return False -- "Quem excele em empregar a força militar subjulga os exércitos dos outros povos sem travar batalha, toma cidades fortificadas dos outros povos sem as atacar e destrói os estados dos outros povos sem lutas prolongadas. Deve lutar sob o Céu com o propósito primordial da 'preservação'. Desse modo suas armas não se embotarão, e os ganhos poderão ser preservados. Essa é a estratégia para planejar ofensivas." -- Sun Tzu, em "A arte da guerra" -- http://mail.python.org/mailman/listinfo/python-list
andmap and ormap
Hello, Does python have andmap and ormap: andmap((lambda t: boolean(t)),L) gives True if boolean(t) is True for all t in L and False otherwise? And ormap((lambda t: boolean(t)),L) gives True if boolean(t) is True for some t in L and False otherwise? One can use a list comprehension like [x for x in L if not(False in map((lambda t: boolean(t)),L))] as an example of selection by andmap, and [x for x in L if (True in map((lambda t: boolean(t)),L))] as an example of selection by ormap. How does one define andmap/ormap so its first argument is a boolean procedure or lambda? def andmap(b,L): if False in map(b,L): return False else: return True def ormap(b,L): if True in map(b,L): return True else: return False Is this good enough? Walter Kehowski -- http://mail.python.org/mailman/listinfo/python-list
