What's the Most Efficient Way to Create Lists of Repeated Single Items in Python?

Creating Lists of Single Item Repetitions

To generate a series of lists containing the same element repeated n times, there are several approaches.

One common method is to employ list comprehension:

[e for number in range(n)]

However, if you seek an alternative approach, consider using the multiplication operator:

[e] * n

While this method effectively duplicates the element e n times, note that if e is an empty list, you will obtain a list with n references to the same list, rather than n separate empty lists.

Performance Considerations

When comparing the time efficiency of different methods, it's often assumed that repeat is superior to [e] * n. However, it's important to recognize that repeat does not immediately create a list. Instead, it returns an object that allows for the creation of a list when necessary.

For a more accurate performance comparison:

timeit.timeit('list(itertools.repeat(0, 10))', 'import itertools', number = 1000000)

This modification reveals that [e] * n is the more efficient solution for generating actual lists. However, if lazily generated elements are desired, repeat remains a viable option.

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