How Can I Efficiently Create Lists with Repeated Elements in Python?

Creating Lists with Repeated Elements in Python

Generating lists with repeating elements is a common task in Python programming. While list comprehensions are a convenient way to accomplish this, other methods exist that can provide greater efficiency or flexibility.

One such method is using the * operator to replicate an element n times. For example, to create a list of 10 zeros, we can simply write:

[0] * 10

This method is particularly useful when the element to be repeated is a mutable object. For instance, in the following code, we create a list of 10 empty lists:

[[]] * 10

In this case, each element of the list is a distinct empty list, unlike when using a list comprehension, where all the elements would refer to the same list.

It's important to note that using * to replicate an element doesn't create a new object for each element. Instead, it creates multiple references to the same object. This can be a performance advantage when the element is a complex object, as it avoids creating multiple copies.

While performance benchmarks initially suggest that the repeat function from the itertools module is faster for creating lists with repeating elements, it's crucial to consider that repeat doesn't actually return a list but an iterator that generates elements lazily. Converting the iterator to a list introduces an additional performance overhead.

Therefore, if the goal is to create a list immediately, using [e] * n is the preferred approach. However, if the elements need to be generated lazily, the repeat function can offer benefits in terms of memory consumption and code readability.

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