How to generate list with repeating items?

Question

Suppose I want to create a list like the following with a list comprehension:

["2", "2", "2", "3", "3", "3", "4", "4", "4"]

I have tried:

>>> [*[str(n)] * 3 for n in range(2, 5)]

  File "<stdin>", line 1
SyntaxError: iterable unpacking cannot be used in comprehension

and

>>> [str(n) * 3 for n in range(2, 5)]
['222', '333', '444']

where I got the numbers, but together in one string, and

>>> [[str(n)] * 3 for n in range(2, 5)]
[['2', '2', '2'], ['3', '3', '3'], ['4', '4', '4']]

where I got a nested list, but want a flat one. Can this be done in a simple way, or do I have to take the nested list method and flatten the list ?

Kevin Eldurson · Accepted Answer · 2021-04-25 20:05:45Z

3

A nested for loop is your best bet. I think this is the simplest solution:

[str(n) for n in range(2, 5) for i in range(3)]

edited Apr 25, 2021 at 20:05

answered Apr 25, 2021 at 20:00

Kevin Eldurson

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2 Comments

TheEagle Over a year ago

OMG, whyever didn't I think of THAT ? Thanks too ! (I'll have a hard time choosing one to accept …)

JonSG Over a year ago

While the accepted answer by @duckboycool is perfectly good and works, I find this answer more intuitive.

duckboycool · Accepted Answer · 2021-04-25 19:58:30Z

1

A simple way you could do this with list comprehension is by using integer division.

[str(n // 3) for n in range(6, 15)]

answered Apr 25, 2021 at 19:58

duckboycool

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1 Comment

TheEagle Over a year ago

Wow, cool, I would never have thought of this ! Thanks a lot !

TheEagle · Accepted Answer · 2021-04-25 20:10:41Z

1

You can use the function chain function from the itertools library in order to flatten the list.

>>> from itertools import chain
>>> list(chain(*[[str(n)] * 3 for n in range(2, 5)]))
['2', '2', '2', '3', '3', '3', '4', '4', '4']

edited Apr 25, 2021 at 20:10

TheEagle

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answered Apr 25, 2021 at 20:00

Marios Mitalidis

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