Python Return List

Do you need to create a function that returns a list but you don’t know how? No worries, in sixty seconds, you’ll know! Go! 👇

Python Return List Basic

A Python function can return any object such as a list. To return a list, first create the list object within the function body, assign it to a variable your_list, and return it to the caller of the function using the keyword operation “return your_list“.

For example, the following code creates a function create_list() that iterates over all numbers 0, 1, 2, …, 9, appends them to the list your_list, and returns the list to the caller of the function:

def create_list():
    ''' Function to return list '''
    your_list = []
    for i in range(10):
        your_list.append(i)

    return your_list

numbers = create_list()
print(numbers)
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Note that you store the resulting list in the variable numbers. The local variable your_list that you created within the function body is only visible within the function but not outside of it.

So, if you try to access the name your_list, Python will raise a NameError:

>>> print(your_list)
Traceback (most recent call last):
  File "C:\Users\xcent\Desktop\code.py", line 9, in <module>
    print(your_list)
NameError: name 'your_list' is not defined

To fix this, simply assign the return value of the function — a list — to a new variable and access the content of this new variable:

>>> numbers = create_list()
>>> print(numbers)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Return List with List Comprehension

There are many other ways to return a list in Python. For example, you can use a list comprehension statement instead that is much more concise than the previous code—but creates the same list of numbers:

def create_list():
    ''' Function to return list '''
    return [i for i in range(10)]


numbers = create_list()
print(numbers)
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

List comprehension is a very useful Python feature that allows you to dynamically create a list by using the syntax [expression context].

You iterate over all elements in a given context “for i in range(10)“, and apply a certain expression, e.g., the identity expression i, before adding the resulting values to the newly-created list.

In case you need to learn more about list comprehension, feel free to check out my explainer video:

A Simple Introduction to List Comprehension in Python

Python Return List Using Lambda Function

An interesting way to return a list from a function is to use lambda functions.

A lambda function is an anonymous function in Python. It starts with the keyword lambda, followed by a comma-separated list of zero or more arguments, followed by the colon and the return expression. Use the square bracket notation [ ... ] or the list() constructor to create and return a list object.

The following code snippet uses a combination of features.

• The lambda function dynamically creates a function object and assigns it to the variable create_list. You can then call the function like before with create_list().
• The list comprehension expression creates a list and return it at the same time in a single line of code—it cannot get more concise than that.

create_list = lambda : [i for i in range(10)]

numbers = create_list()
print(numbers)
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Python Return List of Objects

You can create a function that returns a list of objects using the list comprehension expression in combination with the return keyword like so in your function body: return [Example() for _ in range(n)]

Here’s a minimal example:

class Example(object):
    pass


def return_objects(n):
    return [Example() for _ in range(n)]


print(return_objects(3))

👉 Recommended Tutorial: How to Create a List of Objects in Python?

Python Return List as String

To return a list as a string in Python, use list comprehension to convert each list element to a string and the join() method to convert the list of strings to a single string and return this string.

Here’s a minimal example:

def list_to_string(my_list):
    return ' '.join([str(x) for x in my_list])


print(list_to_string(['Alice', 'is', 18, 'years old']))
# Alice is 18 years old

Note that you can also use a generator expression inside the join() method call instead of a list comprehension to save an additional two (!) characters. 🚀

def list_to_string(my_list):
    return ' '.join(str(x) for x in my_list)

There are many more ways to convert a list to a string as shown in the following tutorial. Check it out! 👇

👉 Recommended Tutorial: Python Convert List to String

Python Return List of Tuples From Two Lists

Challenge: How to create a function that takes two lists of same length and returns a list of tuples whereas the i-th elements of both lists are bundled together in a single tuple of the returned list?

To return a list of tuples from two lists use the expression list(zip(list_1, list_2)) that first bundles together the i-th elements of both lists using the zip() function to obtain an iterable of tuples and second convert the result to a list of tuples using the built-in list() function.

Here’s a minimal example of a function that returns a list of tuples from two lists:

def bundle(list_1, list_2):
    return list(zip(list_1, list_2))

print(bundle([1, 2, 3], ['a', 'b', 'c']))
# [(1, 'a'), (2, 'b'), (3, 'c')]

This approach will also work if the lists have different lengths.

And a similar approach will also work if you have more than two or even a variable number of list arguments for the function by using the asterisk operator * like so:

def bundle(*lists):
    return list(zip(*lists))

print(bundle([1, 2, 3], ['a', 'b', 'c']))
# [(1, 'a'), (2, 'b'), (3, 'c')]

print(bundle([1, 2], [3, 4], [5, 6], [7, 8]))
# [(1, 3, 5, 7), (2, 4, 6, 8)]

Python is beautiful, isn’t it?

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You may be interested in our video and blog guide on the zip() function. Check it out! 👇

👉 Recommended Tutorial: Python Zip Function

Where to Go From Here?

Enough theory. Let’s get some practice!

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Related Tutorials

• Python Return String From Function
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• Python Return Set From Function

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A: An extroverted computer scientist looks at your shoes when he talks to you.