> But on python-ideas, G. Rodola noted the following
> assert \
>     1 == 0, \
>         "error"
[...]
> and requested that the *second* or *middle* line should be reported.

No, I was suggesting (assuming it's reasonably possible in terms of implementation) to report the whole block (3 lines) as-is. 
Note that the same would apply for functions.
For example this:

    self.assertEqual(1, 
                     2)

Currently prints:

    Traceback (most recent call last):
      File "foo.py", line 7, in test_foo
        2)
    AssertionError: 1 != 2

While instead it should:

    Traceback (most recent call last):
      File "foo.py", line 6, in test_foo
        self.assertEqual(1, 
                         2)
    AssertionError: 1 != 2