Initialize the formatter with specified format strings.
Initialize the formatter either with the specified format string, or a
default as described above. Allow for specialized date formatting with
the optional datefmt argument. If datefmt is omitted, you get an
ISO8601-like (or RFC 3339-like) format.
Use a style parameter of ‘%’, ‘{’ or ‘$’ to specify that you want to
use one of %-formatting, str.format() ({}) formatting or
string.Template formatting in your format string.
Changed in version 3.2: Added the style parameter.