Nice!

Can you describe how you got to this solution?

Something is broken?

I only get this error on codewars, not on my local python3 or other online python3 runners:

Traceback (most recent call last):
  File "/workspace/default/tests.py", line 4, in <module>
    test.assert_equals(convert("15", dec, bin), '1111', '"15" dec -> bin');
                       ^^^^^^^^^^^^^^^^^^^^^^^
  File "/workspace/default/solution.py", line 3, in convert
    x = bin(15)
        ^^^^^^^
TypeError: 'str' object is not callable

The code:

def convert(input, source, target):
    x = bin(15)
    print(x)

This assumes all numbers are positive integers

Correct: "No floats or non-positive integers will be passed."

and that the provided list of numbers has two items.

Correct too: "... given an array of minimum 4 positive integers"