["python","list"]
Iterating over every two elements in a list

How do I make a for loop or a list comprehension so that every iteration gives me two elements? l = [1,2,3,4,5,6] for i,k in ???: print str(i), '+', str(k), '=', str(i+k) Output: 1+2=3 3+4=7 5+6=11
Starting with Python 3.12, you can use the batched() function provided by the itertools module: from itertools import batched for x, y in batched(l, n=2): print("%d + %d = %d" % (x, y, x + y)) Otherwise, you need a pairwise() (or grouped()) implementation. 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 itertools documentation, which yields 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, TypeVar T = 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)