File location: python-reference/source/docs/str/formatting.rst.
In Syntax %[key][flags][width][.precision][length type]conversion type % values,
the conversion type is not optional.
It should be Required, which marks the end of the specifier.
I think only the fields in square brackets are optional.
Corresponding docs: https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting
File location: python-reference/source/docs/str/formatting.rst.
In Syntax
%[key][flags][width][.precision][length type]conversion type % values,the
conversion typeis not optional.It should be Required, which marks the end of the specifier.
I think only the fields in square brackets are optional.
Corresponding docs: https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting