How Can I Efficiently Create Lists with Repeated Elements in Python Without List Comprehensions?

Generating Lists with Repeated Elements

In Python, creating multiple lists containing the same repeated elements can be achieved in various ways. This discussion explores a method that bypasses list comprehensions.

Solution:

Python provides the operator * to replicate elements. To create a list filled with n occurrences of element e, simply use the expression [e] * n.

Example:

e = 5
list_of_e = [e] * 10  # [5, 5, 5, 5, 5, 5, 5, 5, 5, 5]

Note:

If e is an empty list, this method will create a list with n references to the same empty list. Providing independent empty lists requires a different approach.

Performance Evaluation:

Although itertools.repeat() may initially appear faster, it requires converting to a list to perform comparisons. The operator * directly returns a list, resulting in better performance:

import timeit
n = 1000000
timeit.timeit('[0] * 10', number=n)  # Faster
timeit.timeit('list(itertools.repeat(0, 10))', number=n)  # Slower

Conclusion:

To create lists of repeated elements without list comprehensions, leverage the * operator, which offers a concise and efficient solution. When requiring lazy generation of elements, consider itertools.repeat().

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