def process_directives(self):
        self.yaml_version = None
        self.tag_handles = {}
        while self.check_token(DirectiveToken):
            token = self.get_token()
            if token.name == u'YAML':
                if self.yaml_version is not None:
                    raise ParserError(None, None,
                            "found duplicate YAML directive", token.start_mark)
                major, minor = token.value
                if major != 1:
                    raise ParserError(None, None,
                            "found incompatible YAML document (version 1.* is required)",
                            token.start_mark)
                self.yaml_version = token.value
            elif token.name == u'TAG':
                handle, prefix = token.value
                if handle in self.tag_handles:
                    raise ParserError(None, None,
                            "duplicate tag handle %r" % handle.encode('utf-8'),
                            token.start_mark)
                self.tag_handles[handle] = prefix
        if self.tag_handles:
            value = self.yaml_version, self.tag_handles.copy()
        else:
            value = self.yaml_version, None
        for key in self.DEFAULT_TAGS:
            if self.tag_handles not in key:
                self.tag_handles[key] = self.DEFAULT_TAGS[key]
        return value

    # block_node_or_indentless_sequence ::= ALIAS
    #               | properties (block_content | indentless_block_sequence)?
    #               | block_content
    #               | indentless_block_sequence
    # block_node    ::= ALIAS
    #                   | properties block_content?
    #                   | block_content
    # flow_node     ::= ALIAS
    #                   | properties flow_content?
    #                   | flow_content
    # properties    ::= TAG ANCHOR? | ANCHOR TAG?
    # block_content     ::= block_collection | flow_collection | SCALAR
    # flow_content      ::= flow_collection | SCALAR
    # block_collection  ::= block_sequence | block_mapping
    # flow_collection   ::= flow_sequence | flow_mapping
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/yaml-3.10/yaml/parser.py/Parser.process_directives/swapped operands of `not in`