How to increment values in a list in python without using the for loop?

Question

in Python how to increment the values in a list without having to write a for loop, e.g.:

group  = [0]*3
item   = [1,2,3]
group += item
print group

to get group = [1,2,3] instead of group = [0,0,0,1,2,3] ?

Something like this might be helpful: http://stackoverflow.com/q/263457/1558022 — alexwlchan, Feb 23 '15 at 13:06
http://stackoverflow.com/questions/14050824/add-sum-of-values-of-two-lists-into-new-list — Tim, Feb 23 '15 at 13:06

Avinash Raj · Answer 1 · 2015-02-23T13:12:58.813

2

You could use numpy module. This won't need a for loop.

>>> import numpy as np
>>> group  = np.array([0]*3)
>>> item   = np.array([1,2,3])
>>> group += item
>>> group
array([1, 2, 3])
>>> list(group)
[1, 2, 3]

edited Feb 23 '15 at 13:12

answered Feb 23 '15 at 13:06

Avinash Raj

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score 1 · Accepted Answer · answered Feb 23 '15 at 13:06

You can do element-wise operations (addition in this case) by using zip within a list comprehension.

>>> group = [0]*3
>>> item   = [1,2,3]
>>> group = [i + j for i,j in zip(group, item)]
>>> group
[1, 2, 3]

This is a general solution if group didn't start out as all zeroes, and you wanted to add the current values with some new values.

How to increment values in a list in python without using the for loop?

2 Answers2