Can someone help me with instances.py?

Good question! At first I thought it was due to the float use in the int addition, since if no floats were present in the input an unnecessary ".0" would be in the output. But removing this didn't pass the challenge. I considered what would happen if only ints or only floats were present, but the code handles this by starting z as an int. I've even tried unindenting the assignment to b since it's only needed after the loop completes, to no avail. There is a potential test case if no numbers were present, then a extraneous "0" would be printed. But the suggested fix in the next paragraph always adds a numeric suffix to the string output and it passes.

The straightforward solution would be to replace the checks for float and int with a simple else: to treat all non-strings as numeric. This passes the challenge.

What's not clear is why the explicit used of type checking for floats and ints causes it not to pass. I don't have access to the test data used in the challenge checker.

EDIT: See comment below. This code should pass, but does not due to floating point precision errors caused by the order in which the numbers are added.

Tagging Craig Dennis to check why this code doesn't pass:

def combiner(x):
    y=""
    z=0
    a=0
    for i in x:
        if isinstance(i, str):
            y += i
        if isinstance(i, float):
             z += i
        if isinstance(i, int):
             a += i
    b=z+a
    return "{}{}".format(y,b)