How to Properly Initialize an Empty List with a Predefined Size in Python?

How to Initialize an Empty List with a Specific Size in Python

Creating an empty list in Python that can hold a certain number of elements is a common task. However, it's important to approach it in the correct way to avoid errors.

Incorrect Method

Attempting to assign values to an empty list using the list index notation (xs[i] = value) can lead to an IndexError due to assigning outside the list's current size.

Solution: Append to an Initialized List

To create an empty list, use the square brackets (xs = []) or the list built-in function (xs = list()). To assign values, use the append method (xs.append(value)).

Example:

xs = [None] * 10  # Creates an empty list of size 10
xs[1] = 5  # Assigns a value to the 2nd element

Alternative Methods:

• range(x): Creates a list with elements from 0 to x-1 (Python 2 only, use list(range(10)) in Python 3).
• Function: Define a function that creates and returns the list using append or list comprehension.

Additional Notes:

• IndexError can also occur when assigning beyond the current size of the list (e.g., xs[15] = value).
• List comprehension allows for creating lists with specific values based on an iterable.

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