[Python-ideas] Adding an optional function argument to all() and any() builtins

MRAB python at mrabarnett.plus.com
Sun Nov 21 21:11:38 CET 2010

On 21/11/2010 19:39, Andy Buckley wrote:
> I may be missing a standard idiom, but it seems to me that the any(...)
> and all(...) builtins are unnecessarily limited by requiring that the
> iterable they take as an argument is already in a form suitable for the
> intended kind of boolean comparison.
> Most of the time, when I want to check that any or all of a collection
> matches some test criterion, my iterable is not already in a valid form
> to pass to any() or all(), and so I either have to explicitly re-code a
> slightly modified version of the builtin, or wastefully use map() to
> apply my test to *all* the items in the list. This is only a few lines
> extra, but IMHO it would make these functions more useful and improve
> the readability of this common idiom if the test function could be
> supplied as an optional argument (which, if None, would default to the
> standard boolean comparison):
> For example, this unclear code:
>      testval = False
>      for i in mylist:
>          if mytestfunction(i):
>              testval = True
>              break
>      if testval:
>          foo()
> or this wasteful (and still unclear, IMO) version:
>      mylist_bool = map(mytestfunction, mylist)
>      if any(mylist_bool):
>          foo()
> would be replaced by the very natural form:
>      if any(mylist, test=mytestfunction):
>          foo()
> The "test" keyword arg is perhaps not the best name, I admit, but no
> other jumps prominently to mind ("match", "fn"?).
> I think this would be a nice feature, and would improve the expressivity
> of the language, much as the "key" optional arg to sort() does. Of
> course, maybe I just don't know the nice way to do these sorts of
> tests... please let me know if I missed something and am reinventing the
> wheel ;)
if any(mytestfunction(i) for i in mylist):

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