>> Doesn't always zeroes == length?> "zeroes" requires "length", but "length" does not require "zeroes".  As it happens all the format units supported by str always have both parameters either True or False.  But the Py_UNICODE converter accepts "length" for format units u# and Z#, and doesn't support "zeroes"."length=True" implies "zeroes=True" in the Py_UNICODE converter. "u" and "Z" don't allow null characters, "u#" and "Z#" allow null characters. "zeroes" doesn't add any information and isn't needed.