Add similar value multiple times in a Python list

There are occasions when we need to add the same value multiple times to a Python list. This is useful for initializing lists, creating test data, or padding sequences. Python provides several built-in methods to achieve this efficiently.

Using the * Operator

This is the most straightforward method. The * operator creates a new list by repeating elements a specified number of times.

Example

Creating a list with repeated strings ?

given_value = 'Hello! '
repeated_list = [given_value] * 5
print(repeated_list)

The output of the above code is ?

['Hello! ', 'Hello! ', 'Hello! ', 'Hello! ', 'Hello! ']

You can also repeat numbers or other data types ?

numbers = [0] * 5
print("Numbers:", numbers)

mixed = [42, 'test'] * 3
print("Mixed:", mixed)

Numbers: [0, 0, 0, 0, 0]
Mixed: [42, 'test', 42, 'test', 42, 'test']

Using itertools.repeat()

The itertools.repeat() function creates an iterator that returns the same value repeatedly. Use list() to convert it to a list.

Example

from itertools import repeat

given_value = 'Hello! '
repeated_list = list(repeat(given_value, 5))
print(repeated_list)

['Hello! ', 'Hello! ', 'Hello! ', 'Hello! ', 'Hello! ']

Using List Comprehension

List comprehension provides a readable way to create repeated values, especially when you need more complex logic.

Example

given_value = 'Hello! '
repeated_list = [given_value for i in range(5)]
print(repeated_list)

# With enumeration
indexed_list = [f"{given_value}{i}" for i in range(3)]
print("Indexed:", indexed_list)

['Hello! ', 'Hello! ', 'Hello! ', 'Hello! ', 'Hello! ']
Indexed: ['Hello! 0', 'Hello! 1', 'Hello! 2']

Comparison

Conclusion

Use the * operator for simple repetition, itertools.repeat() for memory efficiency, and list comprehension when you need to modify values during repetition. Each method creates a new list with the specified number of repeated elements.