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Newsgroups: comp.lang.python
Date: Wed, 23 Jan 2013 21:01:37 -0800 (PST)
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Subject: Re: Arent these snippets equivalent?
From: Coolgg <gauravj123@gmail.com>
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Xref: csiph.com comp.lang.python:37541

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.