# Iterating over every two elements in a list [duplicate]

You need a ** pairwise()** (or

**) implementation.**

`grouped()`

`def pairwise(iterable): "s -> (s0, s1), (s2, s3), (s4, s5), ..." a = iter(iterable) return zip(a, a)for x, y in pairwise(l): print("%d + %d = %d" % (x, y, x + y))`

Or, more generally:

`def grouped(iterable, n): "s -> (s0,s1,s2,...sn-1), (sn,sn+1,sn+2,...s2n-1), (s2n,s2n+1,s2n+2,...s3n-1), ..." return zip(*[iter(iterable)]*n)for x, y in grouped(l, 2): print("%d + %d = %d" % (x, y, x + y))`

In Python 2, you should import `izip`

as a replacement for Python 3's built-in `zip()`

function.

All credit to martineau for his answer to my question, I have found this to be very efficient as it only iterates once over the list and does not create any unnecessary lists in the process.

**N.B**: This should not be confused with the ** pairwise** recipe in Python's own

**documentation, which yields**

`itertools`

`s -> (s0, s1), (s1, s2), (s2, s3), ...`

, as pointed out by @lazyr in the comments.Little addition for those who would like to do type checking with **mypy** on Python 3:

`from typing import Iterable, Tuple, TypeVarT = TypeVar("T")def grouped(iterable: Iterable[T], n=2) -> Iterable[Tuple[T, ...]]: """s -> (s0,s1,s2,...sn-1), (sn,sn+1,sn+2,...s2n-1), ...""" return zip(*[iter(iterable)] * n)`

Well you need tuple of 2 elements, so

`data = [1,2,3,4,5,6]for i,k in zip(data[0::2], data[1::2]): print str(i), '+', str(k), '=', str(i+k)`

Where:

`data[0::2]`

means create subset collection of elements that`(index % 2 == 0)`

`zip(x,y)`

creates a tuple collection from x and y collections same index elements.