Single-element tuples in Python

09 of september of 2024

Single Element Tuples

Disclaimer: This post has been translated to English using a machine translation model. Please, let me know if you find any mistakes.

If in Python we want to create a list with a single element, we simply write the element between square brackets, for example:

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		list = [1]
type(list)
	
	Copied

>_ Output

			
				list

However, with tuples we cannot write an element within parentheses

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		tupla = (1)
type(tupla)
	
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>_ Output

int

As we can see, Python interprets it as an integer, not as a tuple. To solve this, a comma is added after the element, for example:

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		tupla = (1,)
type(tupla)
	
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>_ Output

			
				tuple

What is this for? When we have a function that returns several parameters, what it is actually returning is a tuple. So, it may happen that we have a code that calls a function, checks the length of the returned tuple, and processes each element of the tuple. Let's look at an example

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		def return_tuple():
    return 1, 2, 3
def process_tuple():
    tuple = return_tuple()
    for i in tuple:
        print(i)
process_tuple()
	
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>_ Output

But, what happens in this example if the function doesn't return a tuple? We would get an error

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		def return_int():
    return 1
def process_tuple():
    tuple = return_int()
    for i in tuple:
        print(i)
process_tuple()
	
	Copied

>_ Output

			
				---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[5], line 9
      6     for i in tuple:
      7         print(i)
----> 9 process_tuple()
Cell In[5], line 6, in process_tuple()
      4 def process_tuple():
      5     tuple = return_int()
----> 6     for i in tuple:
      7         print(i)
TypeError: 'int' object is not iterable

We get an error because Python tries to iterate through what the function returns, but since it returns an integer it can't iterate through it. We have two ways to solve this, one is that the processing function checks if a tuple has been returned and in that case processes it, another is that the function that returns values always returns a tuple, even if it is a single element.

	
		
			< >
			Input
		
		
			Python
			
		
	
	
		def return_int():
    return 1,
def process_tuple():
    tuple = return_int()
    for i in tuple:
        print(i)
process_tuple()
	
	Copied

>_ Output

As we see, in the return_int function a , has been placed at the end of the return, so it is returning a tuple with a single element, which is why the process_tuple function will not give an error.

Frequently asked questions

Why do I get "TypeError: 'int' object is not iterable" when doing for i in tuple: on a function's return value?

This happens when a function like def return_int(): return 1 returns a single value: in Python, return 1 produces an int, not a tuple, so the for i in tuple: loop can't iterate over it. The fix is to force the function to return a one-element tuple by adding a trailing comma: return 1, (equivalent to return (1,)), which turns type(tupla) from int into tuple and makes the loop work again.

How do I make a function always return a tuple, even when it only has one value to return?

Just add a comma after the value in the return statement, e.g. return 1, instead of return 1. This matters when another function processes the result with a generic loop (for i in tuple: print(i)) that always expects a tuple, similar to the return 1, 2, 3 pattern in return_tuple(): that way the consuming code doesn't need to check whether it got an int or a tuple.

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