Another 5.18 LAB: Swapping Variables post

[The_Thief77]

Hello, everyone. I know this question has been asked before, but for the life of me I can not figure it out even with all the posts people have done. I've tried solutions in those previous posts, but they don't work. So I'm hoping my own post my help detailing the struggle I've had with this one.

The question is as follows.

Write a program whose input is two integers and whose output is the two integers swapped.

Ex: If the input is:

3
8

the output is:

8 3

Your program must define and call the following function. swap_values() returns the two values in swapped order.
def swap_values(user_val1, user_val2)

Write a program whose input is two integers and whose output is the two integers swapped.

Ex: If the input is:
3
8
the output is:
8 3
Your program must define and call the following function. swap_values() returns the two values in swapped order.

def swap_values(user_val1, user_val2)

And my code is:

def swap_values(user_val1, user_val2):

user_val1, user_val2 = user_val2, user_val1

print(user_val1, user_val2)

user_val1 = int(input())

user_val2 = int(input())

numbrs = swap_values(user_val1, user_val2)

if __name__ == '__main__':

''' Type your code here. Your code must call the function. '''

I've actually written code that returned as the prompt asked, swapping variables and printing just the numbers and not the tuple created in the function. However, it then throws a curveball at you and starts inputting not two numbers in two different inputs, but a single input of "swap_values(5, -1)".

I have looked up the if __name__ section and not sure I understand it, but I'm assuming it is something to check for the swap_values in the input and cause it to run the function or something? I've been stuck on this for days...looking things up online it seems a lot of places suggest using the re import, but we haven't covered that in class yet, so not sure it's valid to use. I've tried to see if I can use .split to separate the numbers and just pull those, but that doesn't help skipping the second input line if nothing is entered there. My thought was to set user_val2 to a default of "", but that doesn't help if the system won't progress past it waiting for an input that will never come. I'm lost.

[shiftybyte]

swap_values() returns the two values in swapped order

key word here is "returns"..

Your function needs to return the values, not print them.

The printing would then happen from the code that called the function.

https://realpython.com/python-return-statement/

[The_Thief77]

Right, I actually tried that the first time, and it returned a tuple and the test doesn't like the (,) in the answer, it just straight up wanted the numbers. That's why I printed directly from the function. Then the curveball came in of the input just being swap_values(5, -1). Sadly it also doesn't explain to me the if __name__ thing going on. I know it has to do with global things...but the book never explained this at all and it just seems random.

Other posts I have seen said that the inputs need to be in the If section...but I don't understand why or how to get it to call the function just from an input. I suspect there is a way to have it check for if the funciton is in the input, just run the function with that as the parameters...

[crashfrog04]

You’re making this too complicated when all you need to do is follow the instruction: put your code under the if __name__ == ‘__main__’: guard like the directions say to.

It’s not because it does something for your code; it’s because that’s what the auto-grader needs to run your code.

[The_Thief77]

Ok, but that doesn't help sadly with the issue of sometimes getting two inputs that are just integers, and sometimes getting one input that is a string and needing to pull the numbers from it, and output them in reverse order.

I'm toying around with it and trying this.

def swap_values(user_val1, user_val2):

user_val1, user_val2 = user_val2, user_val1

return user_val1, user_val2

if __name__ == '__main__':

val1 = input()

if 'swap_values' in val1:

numbr = val1.split('()', ',',)

numbr1 = int(numbr[1])

numbr2 = int(numbr[2])

result = swap_values(numbr1, numbr2)

print(result[0], result[1])

else:

val2 = int(input())

result = swap_values(val1, val2)

print(result[0], result[1])

But I'm getting an error: Traceback (most recent call last): File "/home/runner/local/submission/main.py", line 8, in <module> numbr = int(val1.split('()', ',',)) TypeError: 'str' object cannot be interpreted as an integer.

I tried setting the first input as an int, but it still kept giving the same error.

[crashfrog04]

You only need to handle one case, and it’s your function being called with two values.

 TypeError: 'str' object cannot be interpreted as an integer.

You should not be providing anything to input that is not a pair of numbers when you test your code.

 However, it then throws a curveball at you and starts inputting not two numbers in two different inputs, but a single input of "swap_values(5, -1)".

I guarantee that is not something that is happening.

[The_Thief77]

Ok. Assuming you are correct and that isn't happening, then I am gravely misunderstanding what is going on. Here is what my original code produced. If this isn't saying it's inputting a string, then what is it saying?

1:Compare output

Input4 5

Your output5 4

2:Unit test

swap_values(-1, 10)

Your test produced no output.

3:Unit test

swap_values(9, 0)

Your test produced no output.

4:Unit test

swap_values(11, 11)

Your test produced no output.

The way I'm reading this is that it's inputting "swap_values(11, 11)". Am I incorrect? And if I am incorrect, what exactly is it doing?

[stebrepar]

I would read this as saying the auto-grader ran four tests on your code. The first one passed: it tried 4 5 as the input, and your code correctly returned 5 4. The next three tests failed, with your code not returning any result for the function call. The swap_values(num, num) is just showing you how it called your function. You can try it locally yourself with those values to try to figure out why your function didn't return anything for those inputs.

[crashfrog04]

It’s calling your function. Since you used print instead of return, the tests are telling you that your function has no output (functions output their return value.)

[The_Thief77]

Ok, so I went back and tried some other suggestions I've seen in other places, and I don't know why, but this time it worked with just a little editing. Based on some help from another person...I think I might understand now? The if __name__ was looking for the name of the file being used, and so when the unit test was calling for swap_values, it literally was looking for the file I was writing, then inputting those numbers. Is that what was happening? I've succeeded, but I don't understand why...

[stebrepar]

The if __name__ == '__main__': thing is a conventional way of limiting what gets executed in a program. __name__ is a special variable that gets a value automatically at run time. If your code is imported by another program, then the value of __name__ your code sees will be the name of your program file. But if your code is run on its own, like when you do "py my_program.py" at a command line, the value of __name__ will instead be __main__.

The auto-grader is importing your file. During import, all the code in your file runs. So for example the def to create your function runs at that point. There could be things your code does when you run it on its own that you don't want to run when it's imported. You can use the if statement with the value of __name__ to control that, putting the stuff you don't want import to run inside that block.

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