Assert in python3

Question

when going through some code, I found a line that confused me a little.

assert x.shape == y.shape,(x.shape, y.shape)

I know, that assert x.shape == y.shape is basically a safety check to make sure, x and y have the same shape (i.e. have the same dimensions) But what does the ,(x.shape, y.shape) behind it mean? What is it good for?

Answer 1

That (x.shape, y.shape) is the message to print with the assertion error. Your code would be equivalent of:

if __debug__:
    if not x.shape == y.shape:
        raise AssertionError((x.shape, y.shape))

__debug__ This constant is true if Python was not started with an -O option.