Question

I just extracted some data from a list using python but think it’s overcomplicated and unpythonic and there’s probably a much better way to do this. I’m actually pretty sure I saw this somewhere in the standard library docs but my brain refuses to tell me where.

So here it goes:

Input:

x = range(8) # any even sequence

Output:

[[0, 1], [2, 3], [4, 5], [6, 7]]

My take:

[ [x[i], x[i+1]] for i in range(len(x))[::2] ]

Answer 1

Tuples?

In Python 2.n

>>> zip(*2*[iter(x)])
[(0, 1), (2, 3), (4, 5), (6, 7)]

In Python 3.n

zip() behaves slightly differently…

>> zip(*2*[iter(x)])
<zip object at 0x285c582c>
>>> list(zip(*2*[iter(x)])])
[(0, 1), (2, 3), (4, 5), (6, 7)]

Lists?

The implementation is the same in Python 2 and 3…

>>> [[i,j] for i,j in zip(*2*[iter(x)])]
[[0, 1], [2, 3], [4, 5], [6, 7]]

Or, alternatively:

>>> [list(t) for t in zip(*2*[iter(x)])]
[[0, 1], [2, 3], [4, 5], [6, 7]]

The latter is more useful if you want to split into lists of 3 or more elements, without spelling it out, such as:

>>> [list(t) for t in zip(*4*[iter(x)])]
[[0, 1, 2, 3], [4, 5, 6, 7]]

---

If zip(*2*[iter(x)]) looks a little odd to you (and it did to me the first time I saw it!), take a look at How does zip(*[iter(s)]*n) work in Python?.

See also this pairwise implementation, which I think is pretty neat.