How To Convert a NumPy Array to List in Python

Introduction

With NumPy, np.array objects can be converted to a list with the tolist() function. The tolist() function doesn’t accept any arguments. If the array is one-dimensional, a list with the array elements is returned. For a multi-dimensional array, a nested list is returned.

Prerequisites

In order to complete this tutorial, you will need:

• Familiarity with installing Python 3 and using pip to install packages. And familiarity with coding in Python. How to Code in Python 3 series or using VS Code for Python.

This tutorial was tested with Python 3.9.6 and NumPy 1.23.3.

Converting one-dimensional NumPy Array to List

Let’s construct a one-dimensional array of [1, 2, 3]:

import numpy as np

# 1d array to list
arr_1 = np.array([1, 2, 3])

print(f'NumPy Array:\n{arr_1}')

This code will output:

NumPy Array:
[1 2 3]

Now, let’s use tolist():

import numpy as np

# 1d array to list
arr_1 = np.array([1, 2, 3])

print(f'NumPy Array:\n{arr_1}')

list_1 = arr_1.tolist()

print(f'List: {list_1}')

This new code will output:

List: [1, 2, 3]

The array has been converted from numpy scalars to Python scalars.

Converting multi-dimensional NumPy Array to List

Let’s construct a multi-dimensional array of [ [1, 2, 3], [4, 5, 6] ]:

import numpy as np

# 2d array to list
arr_2 = np.array([[1, 2, 3], [4, 5, 6]])

print(f'NumPy Array:\n{arr_2}')

This code will output:

NumPy Array:
[[1 2 3]
 [4 5 6]]

Now, let’s use tolist():

import numpy as np

# 2d array to list
arr_2 = np.array([[1, 2, 3], [4, 5, 6]])

print(f'NumPy Array:\n{arr_2}')

list_2 = arr_2.tolist()

print(f'List: {list_2}')

This new code will output:

List: [[1, 2, 3], [4, 5, 6]]

The array has been converted from numpy scalars to Python scalars.

Conclusion

In this article, you learned how to use tolist() to convert np.array objects to lists. It is applicable to one-dimensional and multi-dimensional arrays.

References

• API Documentation