Python Mutability

There's also a gotcha with default parameters:

 python

    
def fun(a = []):
    a += [1]
    return a

fun()
print(fun()) # [1, 1]

Wow, nice project!  I'm a 'visual person', I understand better when I see what's happening.

That can help me a lot! :)

As I would expect. Does the result surprise people?

If so, rename the arguments to fun() to be r, s, t, and u. Just inside the function. Does the obvious two scopes now make it clearer?

The fact that x += y modifies lists in place might be surprising if you're expecting it to be exactly equivalent to x = x + y.
- Yes, that is a surprise to many, in other languages 'x+=y' and 'x=x+y' are the same.
- To be fair, I had to read the linked question on SO to understand what was the possible alternative. I do expect that if I use += it is in place.
  On the other hand with Python and Java I always keep forgetting if everything is by value or by reference, I really miss some extra clarity of the languages where you can see if something is mutable when passed to a function
Looks like this whole post is an ad for someone's project. The links hardly have to do with the post.
- The "Solution" link gives the solution to the exercise, the "Explanation" link explains the Python data model concepts behind the exercise. If some parts are hard to understand let me know.
- Yeah and the link went to a site with in-browser remote code execution. Dodgy.
  Clicking Play or GetURL did nothing.
  Luckily my browser is as old as me. And was too grumpy to actually do what it's told.

Here is the link to the code which is being in-browser remote executed

There is no "explanation" next to or within the file. A exercise14.rst or test_exercise14.py would be nice.

The Explanation link provided contains a mountain of visual shit (aka noise) none of which looks like exercise14.py code.

The OP is trying to teach us, i get that. Looks like i'm failing the (mountain of visual shit) reading comprehension section of this exercise.