I would put spaces around + at least. The way you out it, it is not easy to see the end of the first part of the expression.

As hard and senseless as it seems, such are many programming tasks on a real-life project. The requirements and the expected result are not 100% clear. That's why you need to do iterations on different data and finalise the result step by step.

Wouldn't checking the iterable lenght every time make it slower?

I think you are not using variable m.
And too many assignments around n.
I would use more descriptive variable names too.

It's a good practice to specify exception type if you know it.

Before trying to solve this kata, I don't understand how two numeric arguments represent the dimensions of a 2D rectangle. Are these the lengths of two its sides? Can there be a non-2D triangle?

i think clr is not a very good name for an argument

I am not very experienced with Python and may be mistaken, in Python they don't usually have private fields. At least from the materials I read and the code I saw. Unlike Java for example where encapsulation is essential. Or is this just because most people write bad Python code :D