args in PyArg_ParseTuple

[lud]

hello,

i write a module for python and i want to manipulate string with null char
so, i use (in c)
PyArg_ParseTuple(args, "s",&myString) // mystring is a char*
and i get a error message like that :
    type error argument 1: expected string without null byte, string found

can you help me by choose the correct parametre (other than "s" i suppose)

thanks,
ludo