How to use the pyyaml.parser.ParserError function in PyYAML

def parse_flow_mapping_key(self, first=False):
        if not self.check_token(FlowMappingEndToken):
            if not first:
                if self.check_token(FlowEntryToken):
                    self.get_token()
                else:
                    token = self.peek_token()
                    raise ParserError("while parsing a flow mapping", self.marks[-1],
                            "expected ',' or '}', but got %r" % token.id, token.start_mark)
            if self.check_token(KeyToken):
                token = self.get_token()
                if not self.check_token(ValueToken,
                        FlowEntryToken, FlowMappingEndToken):
                    self.states.append(self.parse_flow_mapping_value)
                    return self.parse_flow_node()
                else:
                    self.state = self.parse_flow_mapping_value
                    return self.process_empty_scalar(token.end_mark)
            elif not self.check_token(FlowMappingEndToken):
                self.states.append(self.parse_flow_mapping_empty_value)
                return self.parse_flow_node()
        token = self.get_token()
        event = MappingEndEvent(token.start_mark, token.end_mark)
        self.state = self.states.pop()

event = MappingStartEvent(anchor, tag, implicit,
                            start_mark, end_mark, flow_style=False)
                    self.state = self.parse_block_mapping_first_key
                elif anchor is not None or tag is not None:
                    # Empty scalars are allowed even if a tag or an anchor is
                    # specified.
                    event = ScalarEvent(anchor, tag, (implicit, False), '',
                            start_mark, end_mark)
                    self.state = self.states.pop()
                else:
                    if block:
                        node = 'block'
                    else:
                        node = 'flow'
                    token = self.peek_token()
                    raise ParserError("while parsing a %s node" % node, start_mark,
                            "expected the node content, but found %r" % token.id,
                            token.start_mark)
        return event

def parse_flow_sequence_entry(self, first=False):
        if not self.check_token(FlowSequenceEndToken):
            if not first:
                if self.check_token(FlowEntryToken):
                    self.get_token()
                else:
                    token = self.peek_token()
                    raise ParserError("while parsing a flow sequence", self.marks[-1],
                            "expected ',' or ']', but got %r" % token.id, token.start_mark)
            
            if self.check_token(KeyToken):
                token = self.peek_token()
                event = MappingStartEvent(None, None, True,
                        token.start_mark, token.end_mark,
                        flow_style=True)
                self.state = self.parse_flow_sequence_entry_mapping_key
                return event
            elif not self.check_token(FlowSequenceEndToken):
                self.states.append(self.parse_flow_sequence_entry)
                return self.parse_flow_node()
        token = self.get_token()
        event = SequenceEndEvent(token.start_mark, token.end_mark)
        self.state = self.states.pop()
        self.marks.pop()

def process_directives(self):
        self.yaml_version = None
        self.tag_handles = {}
        while self.check_token(DirectiveToken):
            token = self.get_token()
            if token.name == '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 == 'TAG':
                handle, prefix = token.value
                if handle in self.tag_handles:
                    raise ParserError(None, None,
                            "duplicate tag handle %r" % handle,
                            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 key not in self.tag_handles:

def process_directives(self):
        self.yaml_version = None
        self.tag_handles = {}
        while self.check_token(DirectiveToken):
            token = self.get_token()
            if token.name == '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 == 'TAG':
                handle, prefix = token.value
                if handle in self.tag_handles:
                    raise ParserError(None, None,
                            "duplicate tag handle %r" % handle,
                            token.start_mark)
                self.tag_handles[handle] = prefix
        if self.tag_handles:
            value = self.yaml_version, self.tag_handles.copy()

end_mark = token.end_mark
                    tag = token.value
            elif self.check_token(TagToken):
                token = self.get_token()
                start_mark = tag_mark = token.start_mark
                end_mark = token.end_mark
                tag = token.value
                if self.check_token(AnchorToken):
                    token = self.get_token()
                    end_mark = token.end_mark
                    anchor = token.value
            if tag is not None:
                handle, suffix = tag
                if handle is not None:
                    if handle not in self.tag_handles:
                        raise ParserError("while parsing a node", start_mark,
                                "found undefined tag handle %r" % handle,
                                tag_mark)
                    tag = self.tag_handles[handle]+suffix
                else:
                    tag = suffix
            #if tag == '!':
            #    raise ParserError("while parsing a node", start_mark,
            #            "found non-specific tag '!'", tag_mark,
            #            "Please check 'http://pyyaml.org/wiki/YAMLNonSpecificTag' and share your opinion.")
            if start_mark is None:
                start_mark = end_mark = self.peek_token().start_mark
            event = None
            implicit = (tag is None or tag == '!')
            if indentless_sequence and self.check_token(BlockEntryToken):
                end_mark = self.peek_token().end_mark
                event = SequenceStartEvent(anchor, tag, implicit,

def parse_block_mapping_key(self):
        if self.check_token(KeyToken):
            token = self.get_token()
            if not self.check_token(KeyToken, ValueToken, BlockEndToken):
                self.states.append(self.parse_block_mapping_value)
                return self.parse_block_node_or_indentless_sequence()
            else:
                self.state = self.parse_block_mapping_value
                return self.process_empty_scalar(token.end_mark)
        if not self.check_token(BlockEndToken):
            token = self.peek_token()
            raise ParserError("while parsing a block mapping", self.marks[-1],
                    "expected , but found %r" % token.id, token.start_mark)
        token = self.get_token()
        event = MappingEndEvent(token.start_mark, token.end_mark)
        self.state = self.states.pop()
        self.marks.pop()
        return event