Please ignore this solution--when refactoring I forgot to remove let mut final_string = String::new();

You're right!

I think you weren't supposed to change the 'function signature'.

Thank you.

The exact same question was answered in the third post below yours.

Magnitude is not a method, it should be implemented as a property.

The tests for my solution pass except for exit... curious if this is an issue with the test (code in python):

Traceback (most recent call last):
File "main.py", line 19, in
test.assert_approx_equals(Vector(examples[0]).magnitude, 3.741, 0.001)
File "/runner/frameworks/python/cw-2.py", line 84, in assert_approx_equals
div = max(abs(actual), abs(expected), 1)
TypeError: bad operand type for abs(): 'method'

I didn't change anything- default was set to 3.8, but it ran correctly this time

Currently 3.8 is the only available version.

change the language to 3.8 and it'll work