me too

The details specified are sufficient to solve the problem here ... test your solution and see if it passes the test cases!

I completely agree. I found the wording confusing. I did not know if I was to increment and decrement an element outside of the stack.

spoiler flag! x/

@l2iisk
Did you get resolution on this? I ran into the same issue.
You're kinda going down the wrong path.

Let me know if you need further clarification.

"No additional keys" test checks that the input and output of partial_keys are equal.

Fixed.
Anyway, strange, as the original code used random.choice from the beginning and was only available for python 2.7.

Don't worry :)

You are slightly misunderstanding the concept of 4-connectivity. It doesn't make sense to speak of a "4-connected pixel" without referring to another one. 4-connectivity is the technical way of referring to two pixels being connected either vertically or horizontally (excluding diagonally), but one cannot be either by itself. Here are some examples:

We say these two are 4-connected pixels
+----------+
| *** ** * |
| *xx*** **|
| ** *   * |
|    *     |
+----------+

On the contrary, these are not
+----------+
| **x ** * |
| *x**** **|
| ** *   * |
|    *     |
+----------+

And, of course, neither are these
+----------+
| *** ** * |
| *x*x** **|
| ** *   * |
|    *     |
+----------+

A 4-connected component is a series of pixels which form what is called a "connected component" if we se the image as a graph. This means that if we choose any two points inside the 4-connected component, we can find a path between them jumping only from a pixel to another if they are connected in that way.

An example:

+----------+
| *** ** x |
| ****** xx|
| ** *   x |
|    *     |
+----------+

The kata is retired...

A label can be declared at any point in the code. It's still possible to do execution with labels on the fly, but that'd be quite a bit harder.

No, you're wrong, because the same amount of people that got on got off, so it's wrong to assume it was 0. It affects the following steps, see:

station:    1 2 3  4  5  6  7
got on:     5 3 8  11 19 30 0 
got off:    0 3 3  8  11 19 32
on the bus: 5 5 10 13 21 32 0

I guess the problem is you don't know in the second step how many persons got on the bus, you assumed 0 and that's not the case, you should calculate it given the number of persons got off at the last station.