lambda iter lambda iter creative solution for Chunk by veky - python coding challenges

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lambda iter lambda iter solution in Creative category for Chunk by veky

from itertools import islice
chunking_by = lambda L, n: iter(lambda it=iter(L): list(islice(it, n)), [])

Jan. 11, 2020

Comments:

hao.daniel on July 24, 2020, 12:53 a.m.
Like the way that iter() being used with islice. Very cool! Learn something new.

hao.daniel on July 30, 2020, 4:31 p.m.
Hey, Veky, pardon me if this kind of question is not appropriate for you. Just wonder maybe you can help me learn something more Pythonic here, that's why I post my little utility function for your review/feedback. Thanks in advance! ``` def expand_digits(numbers, n): ''' Expand the list of numbers by "n". See Ex, <pre class='brush: python'>>>> expand_digits([1, 2, 3], 2) => [10, 20, 30] >>> expand_digits([10, 2, 3], 2) => [10, 20, 30] >>> expand_digits([-1.234, -10.002, -1.0], 4) => [-1234, -1000, -1000] ''' if n < 1: raise ValueError(f'{n} must be greater than zero!') result = [] for num in numbers: negative = (num > 0 or -1) num = abs(num) if num < (10**n): num *= (10**n) while num > (10**n) - 1: num //= 10 result.append(int(num) * negative) return result </pre> if name == 'main': L = [1, 2, 3, 40] F = [-1.234, -10.002, -1.0] print(expanddigits(L, 2)) print(expanddigits(F, 4))

veky on July 30, 2020, 4:43 p.m.
Sorry, the function doesn't make sense. You say it's "utility"... how/where do you use it? I can't think of any real usage for such a function. "if a number is less than a thousand, multiply it with a thousand" -- what purpose could it serve? 1234 stays, but 123 becomes 123000 ?! And 0.012 becomes 12.0, still being below a thousand. What's going on here? Of course, "a > b - 1" is probably better written as "a >= b". It's not good to differ in the code and in the message. If you compare n with 1, why do you speak about 0 in the error string? For the name, "expand" is surely totally wrong. Maybe "pad" is what you're looking for? (But it's hard to tell since the spec is nonexistent, and the docstring says 'look at the examples' :-/.)

hao.daniel on July 30, 2020, 4:33 p.m.
My question is that I'm not very happy about my approach, and think it must be some Pythonic (cool lib) that can make this little function more readable, and extensible? If you have minutes, please criticize and "shed some lights". It's much appreciated.

hao.daniel on July 30, 2020, 4:48 p.m.
Thanks, Veky, for your fast reply and questions. (actually, it's one of the hobby things that I wrote to kill time...) The spec. is - "Write a function that accepts a list of numbers and converts them into n digit integers." Agreed. pad_number(?) could be more appropriate. Thanks again for your criticism.

veky on July 30, 2020, 5:06 p.m.
You're killing much more than time with such code. :-P :-D Anyway, so if I get you correctly, <ul> <li>the list is just mapped over, in fact the real function is `def padnumber(x, n): ...` and then your function is just `[padnumber(x, n) for x in L]`, right?</li> <li>the number is not really relevant in terms of scale/size, just its digits are taken? Why not just convert it to a string (`format(x, 'e')`, for example), and take as many digits as you want? The biggest problem in the code is you're trying to present it as an arithmetical operation, when it really isn't one.</li> </ul> Of course, something to think about is that floats are not exact, so it's not really defined what 79th digit of `math.tau` is, for example. :-]

hao.daniel on July 30, 2020, 5:16 p.m.
I got it. "Don't make thing more complex than it looks like?"... A few ways to make it correct now. Many Thanks.

veky on July 30, 2020, 6:22 p.m.
I think that "simple" is a bit misleading. Yes, the solutions at the right abstraction level are usually simpler, but that's just the consequence. The important point is to speak about objects that you really want to speak about. As I usually say, if you want to do something with all the elements from a sequence, <pre class='brush: python'>for element in sequence: do_something(element) </pre> is better than <pre class='brush: python'>for index in range(len(sequence)): do_something(sequence[index]) </pre> not because it's simpler, but because it speaks about elements of a sequence instead of indices (note the bold word in spec). The fact that it's also simpler is just a consequence of Python's great design: it makes you do the right thing most of the time. ;-)

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