def METHOD_NAME(s):
    '''Return a sorted list of the Python replacement fields in the string s.
    e.g. ['{}', '{2}', '{object}', '{target}']
    See http://docs.python.org/library/string.html#formatstrings
    '''
    repl_fields_re = re.compile('\{[^\}]*\}')
    return sorted(repl_fields_re.findall(s))