How to extend / concatenate two iterators in Python

Question

I want to combine two iterators efficiently.

Suppose we have two iterators (in Python3)

l1 = range(10)      # iterator over 0, 1, ..., 9
l2 = range(10, 20)  # iterator over 10, 11, ..., 19

If we convert them to lists, it is easy to concatenate like

y = list(l1) + list(l2)  # 0, 1, ,..., 19

However, this may not be effective.

I would like to do something like

y_iter = l1 + l2  # this does not work

What's a good way to do this in Python3?

+3

ywat May 22 '17 at 15:15

2 answers

you can use the chain () function provided by itertools

itertools.chain ()

+1

Fuji clado May 22 '17 at 15:19

Dan D. · Accepted Answer · 2017-05-22T15:18:30+0000

Use itertools.chain

:

from itertools import chain
y_iter = chain(l1, l2)

It outputs all items from l1

and all items from l2

. Effectively concatenate a sequence of ceded items. In the process, he consumes both.