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From: Joshua Landau <joshua.landau.ws@gmail.com>
Date: Mon, 1 Jul 2013 17:30:46 +0100
Subject: Re: Stupid ways to spell simple code
To: Chris Angelico <rosuav@gmail.com>
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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.")
""")