Lesson Contribution - Swapping variables

[klbarnes20]

I'm a member of The Carpentries staff and I'm submitting this issue on behalf of another member of the community. In most cases, I won't be able to follow up or provide more details other than what I'm providing below.

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1. python-novice-inflammation -

Episode 8 - *https://swcarpentry.github.io/python-novice-inflammation/08-func/index.html
https://swcarpentry.github.io/python-novice-inflammation/08-func/index.html;

• *Creating functions introduces swapping variables under exercise "The
  Old Switcheroo". I would like to suggest mentioning that there is an
  elegant way of swapping variables in python.
  b, a = a, b

[svaberg]

I would like to contribute a pull request that closes this issue as part of my instructor training checkout.

[svaberg]

The original issue (raised by @klbarnes20) is, as I understand it, that swapping variables with the help of a temporary value

temp = a
a = b
b = temp

teaches a non-standard way of swapping variables in Python. The pythonic way of swapping variables is via the

a, b = b, a

idiom as explained in this popular Stack Overflow answer. This idiom in also part of the Additional Exercises but is not introduced in the core lessons.

As I see it, the the core 'gotcha' in this exercise is failing to realise that local variables are created when swap is called. Therefore The Old Switcheroo exercise could be changed as follows:

a = 3
b = 7

def swap(a, b):
    a, b = b, a

swap(a, b)

print(a, b)

The idiomatic version of the swap function would, however, invalidates answer candidate 3-4.

This, and the swap idiom not being part of the core curriculum means that I am
leaning towards simply simply noting in the exercise solution that this idiom exists and point the reader to the Additional Exercises.

[ldko]

This discussion is similar to what was in 460. At that time it was decided not mention a, b = b, a. Do you think we should stick to that and close this issue @maxim-belkin ?

[svaberg]

How about replacing the Switcheroo exercise with another that does not introduce the switching concept at all? Switching is not exactly a basic concept anyhow.