What is the Ellipsis Operator [...] in Python Lists and How Does it Work?

Ellipsis Operator in Lists: A Comprehensive Guide

In Python, the ellipsis operator [...] is a special syntax that represents an arbitrary number of unspecified values within a list. This operator is particularly useful in creating circular references or recursive lists where the list points to itself.

What is [...]?

Consider the following code:

p = [1, 2]
p[1:1] = [p]
print(p)

This code will print:

[1, [...], 2]

Here, [...] represents a list that points to itself. The memory representation of this structure looks like this:

[Image of a circular list in memory]

The first and last elements of the list point to the numbers 1 and 2, while the middle element points to the list itself.

Practical Applications

The ellipsis operator is commonly used in situations where a recursive or circular structure is required. Here are some examples:

• Creating a directory structure recursively:

import os

def create_directory(path, ellipsis):
    if ellipsis in path:
        os.mkdir(os.path.dirname(path))
    else:
        os.makedirs(path)

create_directory('/home/user/directory/[...]/subdirectory', [...])

• Building a linked list:

class Node:
    def __init__(self, data, next=None):
        self.data = data
        self.next = next

head = Node(1)
head.next = Node(2)
head.next.next = Node(3, head)  # Creates a circular linked list

Official Documentation

For further information on the ellipsis operator in Python, refer to the official documentation:

• [List Slicing](https://docs.python.org/3/tutorial/introduction.html#lists)

Conclusion

The ellipsis operator in Python provides a concise way to create circular references or recursive lists. Understanding its representation in memory and practical applications is crucial for effective list manipulation and data structure design.

The above is the detailed content of What is the Ellipsis Operator [...] in Python Lists and How Does it Work?. For more information, please follow other related articles on the PHP Chinese website!