human
Here's a good function header given the following:
I wrote the below code

    def get_position(current_str):
        return (len(fields_str) - len(current_str))
    def parse_field_identifier(fields_str):
        first_char = True
        negated = False
        ident = u''
        while fields_str:
            char = fields_str[0]
            if (char in [u'(', u')', u',']):
                if (not ident):
                    raise FieldsParameterParseError((u"unexpected    char    '%s'    at    position    %d" % (char, get_position(fields_str))))
                if ((ident in [u'*', u'_']) and (char == u'(')):
                    raise FieldsParameterParseError((u"unexpected    char    '%s'    at    position    %d" % (char, get_position(fields_str))))
                return (ident, negated, fields_str)
            elif (char == u'-'):
                if (not first_char):
                    raise FieldsParameterParseError((u"unexpected    char    '%s'    at    position    %d" % (char, get_position(fields_str))))
                negated = True
            elif (char in [u'*', u'_']):
                if (ident and (char == u'*')):
                    raise FieldsParameterParseError((u"unexpected    char    '%s'    at    position    %d" % (char, get_position(fields_str))))
                ident += char
            elif (char.isalnum() or (char == u'_')):
                if (ident == u'*'):
                    raise FieldsParameterParseError((u"unexpected    char    '%s'    at    position    %d" % (char, get_position(fields_str))))
                ident += char
            elif char.isspace():
                raise FieldsParameterParseError((u'unexpected    whitespace    at    position    %d' % get_position(fields_str)))
            else:
                raise FieldsParameterParseError((u"unexpected    char    '%s'    at    position    %d" % (char, get_position(fields_str))))
            first_char = False
            fields_str = fields_str[1:]
        return (ident, negated, fields_str)
    def parse_fields(fields_str, expect_close_bracket=False):
        first_ident = None
       ...

What's a good function header?
assistant
#Here's a good function header.

def parse_fields_parameter(fields_str):