How to assert that a mock function is called with a generator?

I'm using mock with py.test for unittests.

One function under test looks like the one below:

def convert(rows):
    rows = (preprocess(r) for r in rows)
    return batch_process(True, rows)

In the test, I would mock preprocess and batch_process. For preprocess, I use side_effect to configure multiple return values, one for each of the rows.

How do I assert that the second argument passed to batch_process is a generator expression of preprocessed rows?