There are two kinds of format strings in Python: those acceptable to
the Python built-in format operator
%, labelled as
‘python-format’, and those acceptable to the
of the ‘str’ object.
% format strings are described in
Python Library reference /
5. Built-in Types /
5.6. Sequence Types /
5.6.2. String Formatting Operations.
Python brace format strings are described in PEP 3101 – Advanced String Formatting, http://www.python.org/dev/peps/pep-3101/.