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parser.py
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# The following YAML grammar is LL(1) and is parsed by a recursive descent # parser. # # stream ::= STREAM-START implicit_document? explicit_document* STREAM-END # implicit_document ::= block_node DOCUMENT-END* # explicit_document ::= DIRECTIVE* DOCUMENT-START block_node? DOCUMENT-END* # 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 # block_sequence ::= BLOCK-SEQUENCE-START (BLOCK-ENTRY block_node?)* BLOCK-END # indentless_sequence ::= (BLOCK-ENTRY block_node?)+ # block_mapping ::= BLOCK-MAPPING_START # ((KEY block_node_or_indentless_sequence?)? # (VALUE block_node_or_indentless_sequence?)?)* # BLOCK-END # flow_sequence ::= FLOW-SEQUENCE-START # (flow_sequence_entry FLOW-ENTRY)* # flow_sequence_entry? # FLOW-SEQUENCE-END # flow_sequence_entry ::= flow_node | KEY flow_node? (VALUE flow_node?)? # flow_mapping ::= FLOW-MAPPING-START # (flow_mapping_entry FLOW-ENTRY)* # flow_mapping_entry? # FLOW-MAPPING-END # flow_mapping_entry ::= flow_node | KEY flow_node? (VALUE flow_node?)? # # FIRST sets: # # stream: { STREAM-START } # explicit_document: { DIRECTIVE DOCUMENT-START } # implicit_document: FIRST(block_node) # block_node: { ALIAS TAG ANCHOR SCALAR BLOCK-SEQUENCE-START BLOCK-MAPPING-START FLOW-SEQUENCE-START FLOW-MAPPING-START } # flow_node: { ALIAS ANCHOR TAG SCALAR FLOW-SEQUENCE-START FLOW-MAPPING-START } # block_content: { BLOCK-SEQUENCE-START BLOCK-MAPPING-START FLOW-SEQUENCE-START FLOW-MAPPING-START SCALAR } # flow_content: { FLOW-SEQUENCE-START FLOW-MAPPING-START SCALAR } # block_collection: { BLOCK-SEQUENCE-START BLOCK-MAPPING-START } # flow_collection: { FLOW-SEQUENCE-START FLOW-MAPPING-START } # block_sequence: { BLOCK-SEQUENCE-START } # block_mapping: { BLOCK-MAPPING-START } # block_node_or_indentless_sequence: { ALIAS ANCHOR TAG SCALAR BLOCK-SEQUENCE-START BLOCK-MAPPING-START FLOW-SEQUENCE-START FLOW-MAPPING-START BLOCK-ENTRY } # indentless_sequence: { ENTRY } # flow_collection: { FLOW-SEQUENCE-START FLOW-MAPPING-START } # flow_sequence: { FLOW-SEQUENCE-START } # flow_mapping: { FLOW-MAPPING-START } # flow_sequence_entry: { ALIAS ANCHOR TAG SCALAR FLOW-SEQUENCE-START FLOW-MAPPING-START KEY } # flow_mapping_entry: { ALIAS ANCHOR TAG SCALAR FLOW-SEQUENCE-START FLOW-MAPPING-START KEY } __all__ = ['Parser', 'ParserError'] from .error import MarkedYAMLError from .tokens import * from .events import * from .scanner import * class ParserError(MarkedYAMLError): pass class Parser: # Since writing a recursive-descendant parser is a straightforward task, we # do not give many comments here. DEFAULT_TAGS = { '!': '!', '!!': 'tag:yaml.org,2002:', } def __init__(self): self.current_event = None self.yaml_version = None self.tag_handles = {} self.states = [] self.marks = [] self.state = self.parse_stream_start def dispose(self): # Reset the state attributes (to clear self-references) self.states = [] self.state = None def check_event(self, *choices): # Check the type of the next event. if self.current_event is None: if self.state: self.current_event = self.state() if self.current_event is not None: if not choices: return True for choice in choices: if isinstance(self.current_event, choice): return True return False def peek_event(self): # Get the next event. if self.current_event is None: if self.state: self.current_event = self.state() return self.current_event def get_event(self): # Get the next event and proceed further. if self.current_event is None: if self.state: self.current_event = self.state() value = self.current_event self.current_event = None return value # stream ::= STREAM-START implicit_document? explicit_document* STREAM-END # implicit_document ::= block_node DOCUMENT-END* # explicit_document ::= DIRECTIVE* DOCUMENT-START block_node? DOCUMENT-END* def parse_stream_start(self): # Parse the stream start. token = self.get_token() event = StreamStartEvent(token.start_mark, token.end_mark, encoding=token.encoding) # Prepare the next state. self.state = self.parse_implicit_document_start return event def parse_implicit_document_start(self): # Parse an implicit document. if not self.check_token(DirectiveToken, DocumentStartToken, StreamEndToken): self.tag_handles = self.DEFAULT_TAGS token = self.peek_token() start_mark = end_mark = token.start_mark event = DocumentStartEvent(start_mark, end_mark, explicit=False) # Prepare the next state. self.states.append(self.parse_document_end) self.state = self.parse_block_node return event else: return self.parse_document_start() def parse_document_start(self): # Parse any extra document end indicators. while self.check_token(DocumentEndToken): self.get_token() # Parse an explicit document. if not self.check_token(StreamEndToken): token = self.peek_token() start_mark = token.start_mark version, tags = self.process_directives() if not self.check_token(DocumentStartToken): raise ParserError(None, None, "expected '<document start>', but found %r" % self.peek_token().id, self.peek_token().start_mark) token = self.get_token() end_mark = token.end_mark event = DocumentStartEvent(start_mark, end_mark, explicit=True, version=version, tags=tags) self.states.append(self.parse_document_end) self.state = self.parse_document_content else: # Parse the end of the stream. token = self.get_token() event = StreamEndEvent(token.start_mark, token.end_mark) assert not self.states assert not self.marks self.state = None return event def parse_document_end(self): # Parse the document end. token = self.peek_token() start_mark = end_mark = token.start_mark explicit = False if self.check_token(DocumentEndToken): token = self.get_token() end_mark = token.end_mark explicit = True event = DocumentEndEvent(start_mark, end_mark, explicit=explicit) # Prepare the next state. self.state = self.parse_document_start return event def parse_document_content(self): if self.check_token(DirectiveToken, DocumentStartToken, DocumentEndToken, StreamEndToken): event = self.process_empty_scalar(self.peek_token().start_mark) self.state = self.states.pop() return event else: return self.parse_block_node() 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: 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 def parse_block_node(self): return self.parse_node(block=True) def parse_flow_node(self): return self.parse_node() def parse_block_node_or_indentless_sequence(self): return self.parse_node(block=True, indentless_sequence=True) def parse_node(self, block=False, indentless_sequence=False): if self.check_token(AliasToken): token = self.get_token() event = AliasEvent(token.value, token.start_mark, token.end_mark) self.state = self.states.pop() else: anchor = None tag = None start_mark = end_mark = tag_mark = None if self.check_token(AnchorToken): token = self.get_token() start_mark = token.start_mark end_mark = token.end_mark anchor = token.value if self.check_token(TagToken): token = self.get_token() tag_mark = token.start_mark 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, start_mark, end_mark) self.state = self.parse_indentless_sequence_entry else: if self.check_token(ScalarToken): token = self.get_token() end_mark = token.end_mark if (token.plain and tag is None) or tag == '!': implicit = (True, False) elif tag is None: implicit = (False, True) else: implicit = (False, False) event = ScalarEvent(anchor, tag, implicit, token.value, start_mark, end_mark, style=token.style) self.state = self.states.pop() elif self.check_token(FlowSequenceStartToken): end_mark = self.peek_token().end_mark event = SequenceStartEvent(anchor, tag, implicit, start_mark, end_mark, flow_style=True) self.state = self.parse_flow_sequence_first_entry elif self.check_token(FlowMappingStartToken): end_mark = self.peek_token().end_mark event = MappingStartEvent(anchor, tag, implicit, start_mark, end_mark, flow_style=True) self.state = self.parse_flow_mapping_first_key elif block and self.check_token(BlockSequenceStartToken): end_mark = self.peek_token().start_mark event = SequenceStartEvent(anchor, tag, implicit, start_mark, end_mark, flow_style=False) self.state = self.parse_block_sequence_first_entry elif block and self.check_token(BlockMappingStartToken): end_mark = self.peek_token().start_mark 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 # block_sequence ::= BLOCK-SEQUENCE-START (BLOCK-ENTRY block_node?)* BLOCK-END def parse_block_sequence_first_entry(self): token = self.get_token() self.marks.append(token.start_mark) return self.parse_block_sequence_entry() def parse_block_sequence_entry(self): if self.check_token(BlockEntryToken): token = self.get_token() if not self.check_token(BlockEntryToken, BlockEndToken): self.states.append(self.parse_block_sequence_entry) return self.parse_block_node() else: self.state = self.parse_block_sequence_entry return self.process_empty_scalar(token.end_mark) if not self.check_token(BlockEndToken): token = self.peek_token() raise ParserError("while parsing a block collection", self.marks[-1], "expected <block end>, but found %r" % token.id, token.start_mark) token = self.get_token() event = SequenceEndEvent(token.start_mark, token.end_mark) self.state = self.states.pop() self.marks.pop() return event # indentless_sequence ::= (BLOCK-ENTRY block_node?)+ def parse_indentless_sequence_entry(self): if self.check_token(BlockEntryToken): token = self.get_token() if not self.check_token(BlockEntryToken, KeyToken, ValueToken, BlockEndToken): self.states.append(self.parse_indentless_sequence_entry) return self.parse_block_node() else: self.state = self.parse_indentless_sequence_entry return self.process_empty_scalar(token.end_mark) token = self.peek_token() event = SequenceEndEvent(token.start_mark, token.start_mark) self.state = self.states.pop() return event # block_mapping ::= BLOCK-MAPPING_START # ((KEY block_node_or_indentless_sequence?)? # (VALUE block_node_or_indentless_sequence?)?)* # BLOCK-END def parse_block_mapping_first_key(self): token = self.get_token() self.marks.append(token.start_mark) return self.parse_block_mapping_key() 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 <block end>, 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 def parse_block_mapping_value(self): if self.check_token(ValueToken): token = self.get_token() if not self.check_token(KeyToken, ValueToken, BlockEndToken): self.states.append(self.parse_block_mapping_key) return self.parse_block_node_or_indentless_sequence() else: self.state = self.parse_block_mapping_key return self.process_empty_scalar(token.end_mark) else: self.state = self.parse_block_mapping_key token = self.peek_token() return self.process_empty_scalar(token.start_mark) # flow_sequence ::= FLOW-SEQUENCE-START # (flow_sequence_entry FLOW-ENTRY)* # flow_sequence_entry? # FLOW-SEQUENCE-END # flow_sequence_entry ::= flow_node | KEY flow_node? (VALUE flow_node?)? # # Note that while production rules for both flow_sequence_entry and # flow_mapping_entry are equal, their interpretations are different. # For `flow_sequence_entry`, the part `KEY flow_node? (VALUE flow_node?)?` # generate an inline mapping (set syntax). def parse_flow_sequence_first_entry(self): token = self.get_token() self.marks.append(token.start_mark) return self.parse_flow_sequence_entry(first=True) 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() return event def parse_flow_sequence_entry_mapping_key(self): token = self.get_token() if not self.check_token(ValueToken, FlowEntryToken, FlowSequenceEndToken): self.states.append(self.parse_flow_sequence_entry_mapping_value) return self.parse_flow_node() else: self.state = self.parse_flow_sequence_entry_mapping_value return self.process_empty_scalar(token.end_mark) def parse_flow_sequence_entry_mapping_value(self): if self.check_token(ValueToken): token = self.get_token() if not self.check_token(FlowEntryToken, FlowSequenceEndToken): self.states.append(self.parse_flow_sequence_entry_mapping_end) return self.parse_flow_node() else: self.state = self.parse_flow_sequence_entry_mapping_end return self.process_empty_scalar(token.end_mark) else: self.state = self.parse_flow_sequence_entry_mapping_end token = self.peek_token() return self.process_empty_scalar(token.start_mark) def parse_flow_sequence_entry_mapping_end(self): self.state = self.parse_flow_sequence_entry token = self.peek_token() return MappingEndEvent(token.start_mark, token.start_mark) # flow_mapping ::= FLOW-MAPPING-START # (flow_mapping_entry FLOW-ENTRY)* # flow_mapping_entry? # FLOW-MAPPING-END # flow_mapping_entry ::= flow_node | KEY flow_node? (VALUE flow_node?)? def parse_flow_mapping_first_key(self): token = self.get_token() self.marks.append(token.start_mark) return self.parse_flow_mapping_key(first=True) 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() self.marks.pop() return event def parse_flow_mapping_value(self): if self.check_token(ValueToken): token = self.get_token() if not self.check_token(FlowEntryToken, FlowMappingEndToken): self.states.append(self.parse_flow_mapping_key) return self.parse_flow_node() else: self.state = self.parse_flow_mapping_key return self.process_empty_scalar(token.end_mark) else: self.state = self.parse_flow_mapping_key token = self.peek_token() return self.process_empty_scalar(token.start_mark) def parse_flow_mapping_empty_value(self): self.state = self.parse_flow_mapping_key return self.process_empty_scalar(self.peek_token().start_mark) def process_empty_scalar(self, mark): return ScalarEvent(None, None, (True, False), '', mark, mark)