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Python Python Collections (2016, retired 2019) Tuples Tuple Swapping

Flore W
Flore W
4,744 Points
Posted by Flore W
Flore W
4,744 Points

Why does add(5,5) give 10, but if I define tuples = (5,5) and call the function add(tuples) it gives an error?

Following up on Kenneth example in the video, I have written:

def add(*nums):

    total = 0

    for num in nums:

        total += num

    return total

1st case, just as in the video returns 10

print(add(5,5))

2nd case as I am trying to define a separate variable and call the function on the variable, gives me "TypeError: unsupported operand type(s) for +=: 'int' and 'tuple'

tuples = (5,5)

print(add(tuples))

What's the difference between the two cases?

3 Answers

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

When you call "add(5,5)", you are passing two number arguments to the function, which is what it is designed to handle.

But when you call "add(tuples)", you are passing a single argument which is a tuple and not a number. This causes an error when the function internally tries to add the tuple to the numeric variable "total".

There is a built-in function named "sum" that will add together the values in an iterable, you could just call that instead: "sum(tuple)".

Flore W
Flore W
4,744 Points
Flore W
Flore W
4,744 Points

Thanks Steve, but I thought that the add function would take a tuple as argument, isn't it why there is the single * before nums? What does the *nums mean in that case? It only takes the values inside the tuple but not the tuple itself?

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

The * ("gather" or "splat" operator) converts individual arguments into an interable that the loop can work with.

If you did not have the * then the function would work with the tuple, but not with the two (or more) numbers. And in that case it would be the same thing as "sum".

Flore W
Flore W
4,744 Points
Flore W
Flore W
4,744 Points

Thanks, but in that case why don't we write the function as:

def add(a,b):
    return a+b
print(add(5,5))

What is the advantage of using the * and the loop?

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

This version would only work with two arguments. The version with the "splat" operator and the loop will work with any number of arguments.

Flore W
Flore W
4,744 Points
Flore W
Flore W
4,744 Points

Got it thanks!

Tilak Muruduru Divakar
Tilak Muruduru Divakar
6,459 Points
Tilak Muruduru Divakar
Tilak Muruduru Divakar
6,459 Points

When you pass individual values like add(5,5), * in the function definition is packing these values into a touple, so that you are able to iterate over the touple and add each number to the total.

When you do add(tuples), * in the function definition is unpacking the touple you are passing into individual values.

You might wanna try add(*tuples). In this case "tuples" is unpacked and passed to the function as individual values which are packed again in the function definition.

Youssef Moustahib
Youssef Moustahib
7,779 Points
Youssef Moustahib
Youssef Moustahib
7,779 Points

Use add(*tuples)

This will unpack the tuple which is like saying add(5,5)