This looks good, is this still work in progress?

@amueller I think we're done now! The import orders were jumbled up, so I reverted them back to how they were (as per your note in the other PR). Thanks!

Looks good, thanks! Let's wait for CI.

There's a test failure in test_make_union_kwargs

You need to change the expected error message in that test.

@amueller, I'm slightly confused as to how the error message should be modified. I think this is the part that needs fixing:

assert_raise_message(
        TypeError,
        'Unknown keyword arguments: "transformer_weights"',
        make_union, pca, mock, transformer_weights={'pca': 10, 'Transf': 1}
    )

I changed the error message to "make_union() got an unexpected keyword argument 'transformer_weights'". Is this the right way to go? Thanks in advance.

That's exactly right. CI is a bit slow right now, have you run the tests locally? You can do pytest path/to/the/test/file.py to run only that test.

@amueller I was just doing that, and can now confirm that all tests pass on my local. Thank you!