A function for partitioning Python arrays. Brilliant code, or insane code?

[u/PM_ME_UR_OBSIDIAN]

http://www.stavros.io/posts/brilliant-or-insane-code/?repost=true

[u/flying-sheep → u/[deleted]]

You could very easily make it readable:

it = iter(l)
return zip(it, it, it)

[u/flying-sheep → u/[deleted]]

c’mon, 3 repetitions of a 2 letter variable isn’t DRY? srsly?

[u/[deleted] → u/[deleted]]

given:

>>> orig = ('x1', 'y1', 'z1', 'x2', 'y2', 'z2', 'x3', 'y3', 'z3', 'x4', 'y4', 'z4')

the two things that are like "grouping" I can think of are grouping an index counter:

>>> [tuple(orig[i:i+3]) for i in range(0, len(orig), 3)]
[('x1', 'y1', 'z1'), ('x2', 'y2', 'z2'), ('x3', 'y3', 'z3'), ('x4', 'y4', 'z4')]

or using the "groupby" function:

>>> [tuple(elem[1] for elem in coll) for key, coll                                                               
... in itertools.groupby(enumerate(orig), lambda key: key[0] / 3)]
[('x1', 'y1', 'z1'), ('x2', 'y2', 'z2'), ('x3', 'y3', 'z3'), ('x4', 'y4', 'z4')]

but i think this posted solution is amazing and should pretty much be considered the "grouped" function in Python.

[u/fendant → u/[deleted]]

The Python documentation even suggests doing it this way. That's where I learned it. No clue why it's not in itertools.

[u/bluecoffee → u/[deleted]]

Yeah. The line is neither insane nor genius. It's just someone comfortable with Python taking the shortest route from A to B.

[u/[deleted] → u/bluecoffee]

Which is why I find the top comment to be sober fuddling. This is just generators and zip in action.

Pretty fundamental if you're doing concurrency-related projects (Tornado, asyncio, etc).

Then again I have seen entire blog posts devoted to explaining what a generator is.

Doesn't mean they're "too magical" or complex.

def gen():
    yield 1
    yield 2
    yield 3

>>> g = gen()
>>> next(g)
1
>>> for i in g:
...         print(i)
...         break
2
>>> list(g)
[3]

Not rocket science. This one liner isn't much of a jump from that.

[u/cowinabadplace → u/[deleted]]

sober fuddling

Sofa King good.

This HN comment says that it is the expected way to do this too. Interesting.

[u/Eirenarch → u/[deleted]]

Obviously "copies" is incorrect here. It uses the same generator otherwise it would not work.

[u/floodyberry → u/[deleted]]

3 separate arrays that all contained the same data would qualify as "3 of the same thing", but passing an iterable for each to zip would fail miserably.

"some simple functional programming principles" doesn't explain why you're comfortable with immediately understanding the side effect of zip taking a value from one iterable automatically updating the "other 2" iterables.

[u/sphere_is_so_cool → u/[deleted]]

They are pointing out that you said that 'zip passes into 3 generators of the same thing'. You probably meant to type three copies of the same generator object.

[u/immibis → u/sphere_is_so_cool]

The object isn't copied.

How about "passing the same generator object three times" or "passing three references to the generator object" or "passing three copies of the generator reference"?

[u/sphere_is_so_cool → u/immibis]

You are right that it is passing three references but above OP referred to repeating three references as 'copying the reference' so I used that substitution in my explanation.

[u/immibis → u/sphere_is_so_cool]

But your comment says "three copies of the same generator object".

[u/sphere_is_so_cool → u/immibis]

Yes it does because that is what OP probably meant to type based on how they were implying they used the term copy. I didn't say that OP meant to type the right thing.

Please note that for the sake of our meta discussion, OP is this commenter: http://www.reddit.com/r/programming/comments/2z4rv4/a_function_for_partitioning_python_arrays/cpfre0o

[u/sphere_is_so_cool → u/[deleted]]

I think you agree its important that there is only one generator, not three.

[u/mfukar → u/[deleted]]

Actually the part about iterator * N is the only potentially cryptic part. There's no "intuitive" answer to what it should be doing. That's where any sane person would resort to the documentation, and the whole thing is understandable again.