How Can I Create an Empty List with a Predefined Size in Python?

Creating an Empty List with a Specified Size in Python

When working with Python lists, a common task is to create an empty list that can hold a certain number of elements. However, if you attempt to assign values to an empty list directly using indexing (e.g., xs[i] = value), you will encounter an IndexError.

The Problem

In Python, lists cannot be initialized with specific indices. Instead, you must create an empty list and then append elements to it using the append() method.

Solution

To create an empty list that can hold 10 elements, you can use a comprehension with the multiplication operator (*) and None:

xs = [None] * 10

This creates a list of 10 None values. You can now assign values to the list using the append() method:

for i in range(0, 9):
    xs.append(i)

Another way to create an empty list with a fixed size is to use the range() function with the list() constructor:

xs = list(range(0, 10))

Alternatively, you can use list comprehension to generate the desired elements and store them in a list:

xs = [i for i in range(0, 10)]

Additional Notes

• Using xs[i] = value to assign values to a list only works when the list has already been initialized with at least i 1 elements.
• The range() function in Python 3 returns an iterator, while in Python 2 it returns a list.

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