Do you need to create a function that returns a set but you don’t know how? No worries, in sixty seconds, you’ll know! Go! ?
A Python function can return any object such as a set. To return a set, first create the set object within the function body, assign it to a variable your_set
, and return it to the caller of the function using the keyword operation “return your_set
“.
For example, the following code creates a function create_set()
that iterates over all numbers 0, 1, 2, …, 9, adds them to the set your_set
, and returns the set to the caller of the function:
def create_set(): ''' Function to return set ''' your_set = set() for i in range(10): your_set.add(i) return your_set numbers = create_set() print(numbers) # {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
Note that you store the resulting set in the variable numbers
. The local variable your_set
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_set
, Python will raise a NameError
:
>>> print(your_set) Traceback (most recent call last): File "C:UsersxcentDesktopcode.py", line 9, in <module> print(your_set) NameError: name 'your_set' is not defined
To fix this, simply assign the return value of the function — a set — to a new variable and access the content of this new variable:
>>> numbers = create_set() >>> print(numbers) {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
There are many other ways to return a set from a function in Python. For example, you can use a set comprehension statement instead that is much more concise than the previous code—but creates the same set of numbers:
def create_set(): ''' Function to return set ''' return {i for i in range(10)} numbers = create_set() print(numbers) # {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
Set comprehension is a very useful Python feature that allows you to dynamically create a set 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 set.
In case you need to learn more about set comprehension, feel free to check out my explainer video:
Related Article: A Simple Introduction to Set Comprehension in Python
An interesting way to return a set 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 set()
constructor to create and return a set 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_set
. You can then call the function like before withcreate_set()
. - The set comprehension expression creates a set and return it at the same time in a single line of code—it cannot get more concise than that.
create_set = lambda : {i for i in range(10)} numbers = create_set() print(numbers) # {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
Where to Go From Here?
Enough theory. Let’s get some practice!
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