Lists in Python

Question

I noticed that you can multiply list by scalar but the behavior is weird If I multiply:

[2,3,4] * 3

I get:
[2,3,4,2,3,4,2,3,4]
I understand the results but what it's good for? Is there any other weird operations like that?

why down vote? i searched the site and didn't find an answer what does it good for? — Liran Ben Haim
– Liran Ben Haim, Commented Aug 1, 2016 at 9:44

fodma1 · Accepted Answer · 2016-08-01 10:57:09Z

3

The main purpose of this operand is for initialisation. For example, if you want to initialize a list with 20 equal numbers you can do it using a for loop:

arr=[]
for i in range(20):
    arr.append(3)

An alternative way will be using this operator:

arr = [3] * 20

More weird and normal list operation on lists you can find here http://www.discoversdk.com/knowledge-base/using-lists-in-python

edited Aug 1, 2016 at 10:57

fodma1

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answered Aug 1, 2016 at 9:40

Yoav David

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Comments

Swapniel · Accepted Answer · 2016-08-01 09:43:11Z

1

The operation has a use of creating arrays initialized with some value.

For example [5]*1000 means "create an array of length 1000 initialized with 5".

If you want to multiply each element by 3, use

map(lambda x: 3*x, arr)

answered Aug 1, 2016 at 9:43

Swapniel

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1 Comment

Liran Ben Haim Over a year ago

and its just for initialisation? why python writer did so weird operator instead of a simple init function?

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