How To Create An Empty List in Python with a Certain Size – Detailed Guide

Python lists are used to store multiple items in one object.

You can create an empty list in Python with a certain size using the lst = [None] * 10 statement.

In this tutorial, you’ll learn how to create an empty list in python with a certain size.

If You’re in Hurry…

To create an empty list in python, you can store the None value that acts as a placeholder for missing values. None value is used to denote the absence of an actual value.

Use the below statement to create an empty list with the size 5.

Use this method ONLY when you want to store only Non-Reference Type objects.

Code

lst = [None] * 5

lst

Output

[None, None, None, None, None]

Once you’ve created a list, you can add items to the list using the append() method or the extend() method.

If You Want to Understand Details, Read on…

Different methods are available to create an empty list with a certain size python. Let us look at each one in detail.

Using * operator

You can use the None value and the * operator to create an empty list with an n size. The n denotes the size of the empty list.

None value is used to denote the absence of an actual value.

You can use this method when you want to create a list of non-reference types.

Code

The below code is used to create a Python list with a size of 5.

lst = [None] * 5

lst

Output

When you print the empty list, you’ll see the 5 None values, which denote the missing value.

    [None, None, None, None, None]

Assigning Value to The list

This section demonstrates what happens when you create an empty list using the * operator for the reference type objects.

Create an empty list with the []. This is usually a list of lists.

Then assign a value to the first index position using the append method.

lst = [[]] * 5

lst[0].append(1)

lst

When you print the list, you’ll see that the value is assigned to every index. This can be avoided when you use list comprehension to create an empty list for reference types. (explained in next section).

Output

    [[1], [1], [1], [1], [1]]

Using List Comprehension

You can use list comprehension to create an empty list in Python.

The list comprehension offers a short syntax to create a list based on an existing list.

You can use the range() method to iterate a certain number of times and assign an empty list during each iteration.

You can use this method when you want to create a list of reference types.

Code

The code below demonstrates how to create an empty list with the size 5 using the list comprehension method.

lst = [[] for i in range(5)]

lst

Output

When you print the empty list, you’ll see the below output.

    [[], [], [], [], []]

Assigning Value to The List

You can assign a value at the specific index of the empty list using the append() method.

Code

The code below demonstrates assigning a value to the first index position 0 of an empty list.

lst = [[] for i in range(5)]

lst[0].append(1)

lst

Since the empty list is created using the list comprehension method, the value will be assigned ONLY at the specific index.

Output

When you print the empty list, you’ll see the below output.

    [[1], [], [], [], []]

Using Numpy Array

NumPy library provides an empty() function to create an empty list.

You can use this method when you want to store any specific object type in the empty list. By default, a Python list allows you to store the objects of different types. For example, a single list can contain a String, a number, etc.

Installing Numpy

You can use the below pip command to install numpy.

Prefix the % operator to install it directly from the Jupyter notebook.

pip install numpy

Creating An Empty List Using Numpy

You can use the empty() method in the NumPy library to create an empty list.

It accepts two parameters.

  • Size – Size of the empty list to be created
  • dtype – The type of object that needs to be stored in the list. Use dtype=object to store any type of object in the list.

Code

import numpy as np

lst = np.empty(5, dtype=object)

lst

Output

When you print the list, you’ll see the list and its dtype.

    array([None, None, None, None, None], dtype=object)

This is how you can use the NumPy library to create an empty list with a specific size.

Initialize List of Size N with 0

To initialise a Python list of size N with value 0, you can use the below code.

lst = [0] * 10

lst

Output

Each index of the list will contain the value 0.

    [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

Initialize List of Size for Reference Types

This section demonstrates how the * operator and the list comprehension behave differently for the reference type objects.

The below code demonstrates what happens when you use the * operator for the reference type. Assigning a value to a specific index also modifies the values at the other indexes. This is to the reference nature.

lst = [[]] * 5

lst[0].append(1)

lst

Output

    [[1], [1], [1], [1], [1]]

The below code demonstrates what happens when you use the list comprehension for the reference type. Assigning a value to a specific index doesn’t modify the values at the other indexes as well.

lst = [[] for x in range(5)]

lst[0].append(1)

lst

Output

    [[1], [], [], [], []]

Conclusion

You’ve learned how to create an empty list in python with a certain size.

You’ve also learned when to use the * operator, when to use the list comprehension method and when to use the Numpy library to create an empty list with a specific size.

Additionally, you’ve learned how to make a list with N elements with a default value of 0.

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