On Feb 18, 9:37 pm, Kurt Smith <kwmsm...@gmail.com> wrote:
> On Thu, Feb 18, 2010 at 10:46 PM, Steve Howell <showel...@yahoo.com> wrote:
> > On Feb 18, 2:49 pm, Jonathan Gardner <jgard...@jonathangardner.net>
> > wrote:
> >> On Feb 18, 8:15 am, Steve Howell <showel...@yahoo.com> wrote:
>
> >> > def print_numbers()
> >> > [1, 2, 3, 4, 5, 6].map { |n|
> >> > [n * n, n * n * n]
> >> > }.reject { |square, cube|
> >> > square == 25 || cube == 64
> >> > }.map { |square, cube|
> >> > cube
> >> > }.each { |n|
> >> > puts n
> >> > }
> >> > end
>
> >> If this style of programming were useful, we would all be writing Lisp
> >> today. As it turned out, Lisp is incredibly difficult to read and
> >> understand, even for experienced Lispers. I am pleased that Python is
> >> not following Lisp in that regard.
>
> >> for n in range(1,6):
> >> square = n*n
> >> cube = n*n*n
> >> if square == 25 or cube == 64: continue
> >> print cube
>
> > There's definitely a cognitive dissonance between imperative
> > programming and functional programming. It's hard for programmers
> > used to programming in an imperative style to appreciate a functional
> > approach, because functional solutions often read "upside down" in the
> > actual source code and common algebraic notation:
>
> > def compute_squares_and_cubes(lst):
> > return [(n * n, n * n * n) for n in lst]
>
> > def reject_bad_values(lst):
> > return [(square, cube) for (square, cube) \
> > in lst if not (square == 25 or cube == 64)]
>
> > def cubes_only(lst):
> > return [cube for square, cube in lst]
>
> > def print_results(lst):
> > # 1. compute_squares_and_cubes
> > # 2. reject_bad_values
> > # 3. take cubes_only
> > # 4. print values
> > for item in \
> > cubes_only( # 3
> > reject_bad_values( # 2
> > compute_squares_and_cubes(lst))): # 1
> > print item # 4
>
> > You can, of course, restore the natural order of operations to read
> > top-down with appropriate use of intermediate locals:
>
> > def print_results(lst):
> > lst2 = compute_squares_and_cubes(lst)
> > lst3 = reject_bad_values(lst2)
> > lst4 = cubes_only(lst3)
> > for item in lst4:
> > print item
>
> > --
> >http://mail.python.org/mailman/listinfo/python-list
>
> # sent the original to the wrong place -- resending to python-list.
>
> Somewhat off topic, but only somewhat: you could use coroutines to
> get a pipeline effect.
>
> #--------------8<-----------------------------
> # Shamelessly lifted from David Beazley's
> # http://www.dabeaz.com/coroutines/
>
> def coroutine(co):
> def _inner(*args, **kwargs):
> gen = co(*args, **kwargs)
> gen.next()
> return gen
> return _inner
>
> def squares_and_cubes(lst, target):
> for n in lst:
> target.send((n * n, n * n * n))
>
> @coroutine
> def reject_bad_values(target):
> while True:
> square, cube = (yield)
> if not (square == 25 or cube == 64):
> target.send((square, cube))
>
> @coroutine
> def cubes_only(target):
> while True:
> square, cube = (yield)
> target.send(cube)
>
> @coroutine
> def print_results():
> while True:
> print (yield)
>
> squares_and_cubes(range(10),
> reject_bad_values(
> cubes_only(
> print_results()
> )
> )
> )
Wow! It took me a while to get my head around it, but that's pretty
cool.
--
http://mail.python.org/mailman/listinfo/python-list
