https://docs.python.org/3/reference/lexical_analysis.html#f-strings

The description of the "=" functionality says:

By default, the '=' causes the repr() of the expression to be provided, unless there is a format specified. When a format is specified it defaults to the str() of the expression unless a conversion '!r' is declared.

But that's not correct. If a format is specified, it uses value.__format__(format_spec).

I'll produce a patch.