How Does Ellipsis (...) Work in Python Lists?

Understanding Ellipsis [...] in Python Lists

When working with lists in Python, you may have encountered the ellipsis symbol [...]. This symbol serves as a placeholder for an omitted list of elements and can be used for various purposes.

Consider the following code snippet:

p = [1, 2]
p[1:1] = [p]

The output of this code is:

[1, [...], 2]

Here, the ellipsis [...] represents a reference to the list p itself. The modified list now contains a circular reference to its own elements.

Memory Representation of Ellipsis

The ellipsis in a list is internally represented as a special object that points to the list it belongs to. This object occupies a single memory address and serves as a placeholder for the omitted elements.

Use Cases of Ellipsis

Ellipsis can be useful in situations where you need to insert or remove a list of elements recursively. For instance, you can create nested lists of lists by using ellipsis as a placeholder for the inner list:

p = [1, [2, [3, 4, 5]]]

Official Documentation

For further information on ellipsis in Python, you can refer to the official Python documentation at:

https://docs.python.org/3/library/stdtypes.html?highlight=ellipsis#list.ellipsis

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