On Wednesday, January 23, 2013 6:38:54 PM UTC-8, Terry Reedy wrote:
> On 1/23/2013 6:29 PM, Tim Chase wrote:
>
> > On 01/23/13 16:47, Roy Smith wrote:
>
> >> while getchar() as c:
>
> >> putchar(c)
>
> >>
>
> >> That would give people (including me) the use case they're after most of
>
> >> the time (call a function, assign the return value, and test it). It's
>
> >> way less klunky than:
>
> >>
>
> >> while True:
>
> >> c = getchar()
>
> >> if c:
>
> > # I presume you mean "if not c:" here.
>
> >> break
>
> >> putchar()
>
> >
>
> > I was a pretty strong advocate early in one of these long threads, and
>
> > for the simple cases, it's some attractive syntactic sugar. However, I
>
> > found that it quickly blossomed into a lot of really ugly edge cases
>
> > (multiple tests, multiple results, checking for "is None" vs. false'ness
>
> > or some other condition such as "< 0"). I found that it was pretty easy
>
> > to create a generator-wrapper for this:
>
> >
>
> > def getter(fn):
>
> > while True:
>
> > val = fn()
>
> > if not val: break
>
> > yield val
>
> >
>
> > # DB example
>
> > cursor = conn.cursor()
>
> > for row in getter(lambda: cursor.fetchmany()):
>
> > do_something(row)
>
> >
>
> > # your getchar example
>
> > for c in getter(getchar):
>
> > do_something_else(c)
>
> >
>
> > This allowed me to have both the readability and customized tests (and
>
> > the ability to return multiple values). It could be expanded with
>
> >
>
> > def getter(fn, is_at_end=lambda v: not v):
>
> > while True:
>
> > val = fn()
>
> > if is_at_end(val): break
>
> > yield val
>
> >
>
> > which would even allow you to do things like
>
> >
>
> > for line in getter(file("foo.txt"), lambda s: s.find("xxx") < 0):
>
> > print "This line has 'xxx' in it:"
>
> > print line
>
> >
>
> > and those felt a lot more pythonic than any of the proposals I saw on
>
> > the list.
>
>
>
> I agree. To me, the beauty of iterators and for loops is that they
>
> separate production of the items of a collection from the processing of
>
> the same items. The two processes are often quite independent, and
>
> separating them clearly allows us to mix and match. For instance, when
>
> summing numbers, the internal details of producing the numbers does not
>
> matter.
>
>
>
> --
>
> Terry Jan Reedy
Thanks for all the perspectives everyone. I was just curious about the
functional equivalence and I got what I needed.
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