I prepared a patch to make the check when there is only one dict, it may be the less surprising change.

BTW, I got lost when looking for the root cause  of this change because grepping for the error message did not work as it has line breaks:

-                            PyErr_Format(PyExc_TypeError,
-                                    "%.200s%.200s got multiple "
-                                    "values for keyword argument '%U'",
-                                    PyEval_GetFuncName(func),
-                                    PyEval_GetFuncDesc(func),
-                                    key);

Can we add a note like https://www.kernel.org/doc/html/v4.12/process/coding-style.html#breaking-long-lines-and-strings to the PEP7?

> However, never break user-visible strings such as printk messages, because that breaks the ability to grep for them.

It would help in such situations.