Sentry Answers>Python>

Declare an array in Python

Declare an array in Python

David Y.

The ProblemJump To Solution

How do I declare an array in Python?

The Solution

The default array type in Python is known as a list. To create a new empty list and assign it to a variable, we can use either of the following equivalent lines:

Click to Copy
my_list = [] my_list = list()

We don’t have to instantiate our list as empty but can add any number of items of any type to it.

Click to Copy
my_list = [1, "hello", True]

To create a list with many copies of the same value, we can use the multiplication operator:

Click to Copy
my_list = [0] * 10 # will create a list containing ten 0s.

Note, using this syntax for more complex types can cause issues as the list is created as a reference copy.

Click to Copy
basic = [1] my_list = [basic]*10 print(my_list) # [[1], [1], [1], [1], [1], [1], [1], [1], [1], [1]] basic[0] = 2 print(my_list) # [[2], [2], [2], [2], [2], [2], [2], [2], [2], [2]]

Lists in Python can contain elements of different data types and do not have a predefined length. Python provides an array module that can be used to create lists that can only contain one type of element, though they can also be of arbitrary and varying lengths.

Click to Copy
from array import array my_int_array = array('i', [1, 2, 3, 4, 5]) # create an array of signed integers my_int_array.append(6) # will add 6 to the end of the array my_int_array.append('a') # will throw a TypeError: an integer is required (got type str)
  • Sentry BlogPython Performance Testing: A Comprehensive Guide
  • Sentry BlogLogging in Python: A Developer’s Guide
  • logo
    Listen to the Syntax Podcast

    Tasty Treats for Web Developers brought to you by Sentry. Web development tips and tricks hosted by Wes Bos and Scott Tolinski

    Listen to Syntax

Loved by over 4 million developers and more than 90,000 organizations worldwide, Sentry provides code-level observability to many of the world’s best-known companies like Disney, Peloton, Cloudflare, Eventbrite, Slack, Supercell, and Rockstar Games. Each month we process billions of exceptions from the most popular products on the internet.

© 2024 • Sentry is a registered Trademark
of Functional Software, Inc.