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Date: Mon, 1 Jul 2013 20:36:29 +0100
From: Marcin Szamotulski <mszamot@gmail.com>
To: Joshua Landau <joshua.landau.ws@gmail.com>
Subject: Re: Stupid ways to spell simple code
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On 17:30 Mon 01 Jul     , Joshua Landau wrote:
> On 1 July 2013 14:14, Chris Angelico <rosuav@gmail.com> wrote:
> > On Mon, Jul 1, 2013 at 10:59 PM, Neil Cerutti <neilc@norwich.edu> wrote:
> >> On 2013-06-30, Chris Angelico <rosuav@gmail.com> wrote:
> >>> So, here's a challenge: Come up with something really simple,
> >>> and write an insanely complicated - yet perfectly valid - way
> >>> to achieve the same thing. Bonus points for horribly abusing
> >>> Python's clean syntax in the process.
> >>>
> >>> Go on, do your worst!
> >>
> >> I've often thought it was redundant for Python to support 'if'
> >> when it has dictionaries, cf the rationale for having no
> >> 'switch'.
> >>
> >> valid_name = None
> >> while not valid_name:
> >>     name = input("Enter your name: ")
> >>     valid_name = {
> >>         True: lambda: print("No name longer than 20 letters."),
> >>         False: lambda: True,
> >>     }[len(name) > 20]()
> >>
> >> Much better.
> >
> > Good! Good! But, waaaah. Waaaah.
> >
> > def get_name():
> >   while True:
> >     name = input("Enter your name: ")
> >     yield {
> >         True: lambda: print("No name longer than 20 letters."),
> >         False: lambda: name,
> >     }[len(name) > 20]()
> > name = next(filter(None,get_name()))
> 
> Oh, cruel. But you can do worse. Who needs "while" when you have
> filter(iter(FUNCTION, object()))?
> 
> def get_name():
>     name = input("Enter your name: ")
>     return [
>         lambda: name,
>         lambda: print("No name longer than 20 letters."),
>     ][len(name) > 20]()
> 
> name = next(filter(None, iter(get_name, object())))
> 
> 
> But who needs *any* of this! Defining functions is so old-hat. It's
> all already in the standard library (using only assignments and function-calls):
> 
> from functools import partial
> from operator import getitem, ge, methodcaller
> from itertools import compress, tee
> apply = methodcaller("__call__")
> ret_true = partial(getitem, [True], 0)
> print_invalid = partial(print, "No name longer than 20 letters.")
> inputs = iter(partial(input, "Enter your name: "), ...)
> inputs, valid = tee(inputs)
> valid = map(len, valid)
> valid = map(partial(ge, 20), valid)
> side_effect_valid = map(partial(getitem, [print_invalid, ret_true]), valid)
> side_effect_valid = map(apply, side_effect_valid)
> valid_inputs = compress(inputs, side_effect_valid)
> name = next(valid_inputs)
> 
> 
> Which can be "neatly" expressed as two statements (I'm struggling to
> got it to one without those evil lambdas):
> 
> from functools import partial
> from operator import getitem, ge, methodcaller
> from itertools import compress, tee
> 
> inputs, valid = tee(iter(partial(input, "Enter your name: "), ...))
> 
> name = next(
>     compress(
>         inputs,
>         map(
>             methodcaller("__call__"),
>             map(
>                 partial(
>                     getitem,
>                     [
>                         partial(print, "No name longer than 20 letters."),
>                         partial(getitem, [True], 0)
>                     ]
>                 ),
>                 map(
>                     partial(ge, 20),
>                     map(len, valid)
>                 )
>             )
>         )
>     )
> )
> 
> 
> Beautiful, see?
> 
> 
> Of course, the most powerful function deals with this much more quickly:
> 
> exec("""
> while True:
>     name = input("Enter your name: ")
> 
>     if len(name) <= 20:
>         break
> 
>     else:
>         print("No name longer than 20 letters.")
> """)
> -- 
> http://mail.python.org/mailman/listinfo/python-list


Here is another example which I came across when playing with
generators, the first function is actually quite useful, the second
generator is the whole fun:

from functools import wraps
def init(func):
    """decorator which initialises the generator
    """
    @wraps(func)
    def inner(*args, **kwargs):
        g = func(*args, **kwargs)
        g.send(None)
        return g
    return inner

@init
def gen(func):
     x = (yield)
     while True:
         x = (yield func(x))


now if you have function f
def f(arg):
    return arg**2

then calling f(5) is the same as

g = gen(f)
g.send(5)


I wrote a blog post where I did include this as a `useless` example:
http://pycorner.herokuapp.com/blog/5

Best regards,
Marcin