@classmethod<EOL><INDENT>def str_to_tuple(cls, string):<DEDENT>
parts = string.split('<STR_LIT:/>', <NUM_LIT:2>)<EOL>return tuple((int(parts[i]) if i < len(parts) else None) for i in range(<NUM_LIT:3>))<EOL>
Converts a string in the format xxx/yyy to a (project, activity) tuple, or a string in the format xxx/yyy/zzz
to a (project, activity, role) tuple. Raise `ValueError` if the given `string` contains any component that is
not numeric.