Returning particular output from Python function

November 11, 2022

Suppose, in MATLAB, I have the following function:

function [sums, diff, prod] = myFun(a, b)  
    sums = a + b;
    diff = a - b;
    prod = a * b;
end

If I just wanted to return, say diff, I’d type in the console [~, diff, ~] = myFun(6, 2) and it returns 4.

Now, if I write a similar thing in Python 3.10 (for purposes of this question, I’m using the Spyder IDE):

def myFun(a, b):
    sums = a + b
    diff = a - b
    prod = a * b
    return sums, diff, prod

I can type sum, diff, prod = myFun(5, 3) and I get the results stored in the workspace. If I only want the output prod from this function, is there a way to do this in a way similar to MATLAB? If not, how would I achieve this?

I would prefer to not store all outputs of the function in a tuple and access a desired element later, but to achieve something as slick as the MATLAB usage for a placeholder output.

>Solution :

Your function returns a tuple containing all three values.

You can unpack that tuple in a number of ways that might meet your requirements:

_, _, prod = myFun(3, 4)
print (prod)
# result: 12

Or you could just extract the third item in the tuple:

prod = myFun(3, 4)[2]
print (prod)
# result: 12

Using _, diff, _ = doesn’t really do anything different from sums, diff, prod =, you’re still taking the three values in the tuple and assigning them to three variable names – it just so happens that one of those variable names is an underscore _, and you reuse it, so if you try to return the value of _ afterwards – it’ll return the value that was assigned to it last.

Just for fun you could take a fairly heavy handed approach to making accessing individual results more convenient by using something like namedtuple:

def myFun(a, b):
    from collections import namedtuple
    result = namedtuple('myFun_return', ['sums', 'diff', 'prod'])
    result.sums = a + b
    result.diff = a - b
    result.prod = a * b
    
    return result

prod = myFun(3, 4).prod
print (prod)
#result: 12

result in this context, would be a namedtuple, and you could access its three attributes – sums, diff, and prod by simply calling them on the result, without having to remember the order or anything. But like I said, that is a fairly hefty approach to something so minor…

Resources:
https://www.pythontutorial.net/python-basics/python-unpacking-tuple/
https://www.w3schools.com/python/python_tuples_unpack.asp