fix: correct bug with repeated substation in TransformGrid._add_bus

[danielolsen]

Purpose

Fix an Exception that's thrown when you add two new buses with the same coordinates.

What the code is doing

In TransformGrid the latlon2sub variable holds a dictionary of {(lat, lon): list_of_substation_ids}. When we add a bus at a new location, we create a new substation, and we want to add its id to this lookup dict, but we had been adding it as an int, rather than a list containing that int.

test_transform_grid is updated to check for this bug.

Testing

The unit test is updated to check for this bug, and after the fix all tests pass again.

Time estimate

2 minutes.

[BainanXia]

Good catch!

[danielolsen]

Good catch!

I caught it the hard way 😩

[rouille]

Where is the Exception raised when you add two buses at the same location?

[danielolsen]

Where is the Exception raised when you add two buses at the same location?

sub_id = latlon2sub[(lat, lon)][0] within TransformGrid._add_bus. We get IndexError: invalid index to scalar variable. when we try to add the second new bus, since we try to [0] into an int.