Initialize a list with same values in Python

This post will discuss how to initialize a list with the same values in Python.

1. Using `[e]*n` Syntax

To initialize a list of immutable items, such as None, strings, tuples, or frozensets with the same value, you can do something as:

if __name__ == '__main__':

val = 1

size = 5

a = [val] * size

print(a) # [1, 1, 1, 1, 1]

Download Run Code

For mutable items, never use [e]*n. This will result in the list containing the same object e repeated N times and referencing errors.

2. Using List Comprehensions

For mutable items, like list, set, and dictionary, the most Pythonic solution is to use list comprehensions. You can simply do this as:

if __name__ == '__main__':

val = []

size = 5

a = [val for _ in range(size)] # _ is throwaway variable name

print(a) # [[], [], [], [], []]

Download Run Code

3. Using itertools

The itertools module has a repeat() function that makes an iterator that returns the object over and over again. This faces the same problem as [e]*n and should be best avoided for mutable items.

import itertools

if __name__ == '__main__':

val = 1

size = 5

a = list(itertools.repeat(val, size))

print(a) # [1, 1, 1, 1, 1]

Download Run Code

That’s all about initializing a list with the same values in Python.

Also See:

Initialize list of lists in Python

Initialize a list with same values in Python

1. Using [e]*n Syntax

2. Using List Comprehensions

3. Using itertools

Share this:

1. Using `[e]*n` Syntax