Python : How to Create a List and Initialize with Same Values

In Python Data Structures, a list is a type of container that is used to store multiple pieces of data at the same time. In Python, unlike Sets, the list is ordered and has a definite count. A list’s elements are indexed in a specific order, and the indexing of a list begins with 0 as the first index.

This article will go over various methods to create a list and Initialize with same values.

Examples:

Input:

size=5 , value="BTechGeeks"

Output:

['BTechGeeks', 'BTechGeeks', 'BTechGeeks', 'BTechGeeks', 'BTechGeeks']

Make a list and fill it with the same values

There are several ways create a list and initialize with same values some of them are:

Using [] and multiply operator
Using List Comprehension and range()
Using itertools repeat() function

Method #1:Using [] and multiply operator

Assume we want to make a list of strings that contains 5 identical strings, such as ‘BTechGeeks’.

You can do the following to initialize a list of immutable items, such as None, strings, tuples, or frozensets, with the same value:

# Function which converts list to string
def createList(size, value):
    # Using multiply operator
    requiredlist = [value]*size
    # return the list
    return requiredlist


# Driver code
# given value and size
size = 5
value = "BTechGeeks"
# passing value and size to createList function
print(createList(size, value))

Output:

['BTechGeeks', 'BTechGeeks', 'BTechGeeks', 'BTechGeeks', 'BTechGeeks']

[‘BTechGeeks’] will generate a list with a single value, which we can then multiply by 5. It will loop through the contents of the list 5 times.

Note: Never use [e]*n for mutable items. As a result, the list will contain the same object e repeated N times, as well as referencing errors.

Method #2:Using List Comprehension and range()

List comprehension is a simple and compact syntax for creating a list from a string or another list in Python. It’s a quick way to make a new list by performing an operation on each item in the existing one. List comprehension is much faster than using the for loop to process a list.

The for loop in this list comprehension will iterate over the range object 5 times, adding ‘BTechGeeks’ to the list with each iteration.

Below is the implementation:

# Function which converts list to string
def createList(size, value):
    # Using list comprehension and range
    requiredlist = [value for i in range(size)]
    # return the list
    return requiredlist


# Driver code
# given value and size
size = 5
value = "BTechGeeks"
# passing value and size to createList function
print(createList(size, value))

Output:

['BTechGeeks', 'BTechGeeks', 'BTechGeeks', 'BTechGeeks', 'BTechGeeks']

Method #3: Using itertools repeat() function

The itertools package contains a repeat() function that creates an iterator that returns the object repeatedly. This has the same issue as [e]*n and should be avoided when dealing with mutable items.

Below is the implementation:

#importing itertools
import itertools

# Function which converts list to string
def createList(size, value):
    # Using repeat()
    requiredlist = list(itertools.repeat(value, size))
    # return the list
    return requiredlist


# Driver code
# given value and size
size = 5
value = "BTechGeeks"
# passing value and size to createList function
print(createList(size, value))

Output:

['BTechGeeks', 'BTechGeeks', 'BTechGeeks', 'BTechGeeks', 'BTechGeeks']

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