# 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)
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