gettext: python-format
15.3.3 Python Format Strings
----------------------------
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 ‘format’ method of the ‘str’ object.
Python ‘%’ format strings are described in Python Library reference /
5. Built-in Types / 5.6. Sequence Types /
5.6.2. String Formatting Operations.
<https://docs.python.org/2/library/stdtypes.html#string-formatting-operations>.
Python brace format strings are described in
PEP 3101 – Advanced String Formatting,
<https://www.python.org/dev/peps/pep-3101/>.