content: 
  __all__ = ['BaseConstructor', 'SafeConstructor', 'Constructor',
      'ConstructorError']
  
  from .error import *
  from .nodes import *
  
  import collections.abc, datetime, base64, binascii, re, sys, types
  
  class ConstructorError(MarkedYAMLError):
      pass
  
  class BaseConstructor:
  
      yaml_constructors = {}
      yaml_multi_constructors = {}
  
      def __init__(self):
          self.constructed_objects = {}
          self.recursive_objects = {}
          self.state_generators = []
          self.deep_construct = False
  
      def check_data(self):
          # If there are more documents available?
          return self.check_node()
  
      def get_data(self):
          # Construct and return the next document.
          if self.check_node():
              return self.construct_document(self.get_node())
  
      def get_single_data(self):
          # Ensure that the stream contains a single document and construct it.
          node = self.get_single_node()
          if node is not None:
              return self.construct_document(node)
          return None
  
      def construct_document(self, node):
          data = self.construct_object(node)
          while self.state_generators:
              state_generators = self.state_generators
              self.state_generators = []
              for generator in state_generators:
                  for dummy in generator:
                      pass
          self.constructed_objects = {}
          self.recursive_objects = {}
          self.deep_construct = False
          return data
  
      def construct_object(self, node, deep=False):
          if node in self.constructed_objects:
              return self.constructed_objects[node]
          if deep:
              old_deep = self.deep_construct
              self.deep_construct = True
          if node in self.recursive_objects:
              raise ConstructorError(None, None,
                      "found unconstructable recursive node", node.start_mark)
          self.recursive_objects[node] = None
          constructor = None
          tag_suffix = None
          if node.tag in self.yaml_constructors:
              constructor = self.yaml_constructors[node.tag]
          else:
              for tag_prefix in self.yaml_multi_constructors:
                  if node.tag.startswith(tag_prefix):
                      tag_suffix = node.tag[len(tag_prefix):]
                      constructor = self.yaml_multi_constructors[tag_prefix]
                      break
              else:
                  if None in self.yaml_multi_constructors:
                      tag_suffix = node.tag
                      constructor = self.yaml_multi_constructors[None]
                  elif None in self.yaml_constructors:
                      constructor = self.yaml_constructors[None]
                  elif isinstance(node, ScalarNode):
                      constructor = self.__class__.construct_scalar
                  elif isinstance(node, SequenceNode):
                      constructor = self.__class__.construct_sequence
                  elif isinstance(node, MappingNode):
                      constructor = self.__class__.construct_mapping
          if tag_suffix is None:
              data = constructor(self, node)
          else:
              data = constructor(self, tag_suffix, node)
          if isinstance(data, types.GeneratorType):
              generator = data
              data = next(generator)
              if self.deep_construct:
                  for dummy in generator:
                      pass
              else:
                  self.state_generators.append(generator)
          self.constructed_objects[node] = data
          del self.recursive_objects[node]
          if deep:
              self.deep_construct = old_deep
          return data
  
      def construct_scalar(self, node):
          if not isinstance(node, ScalarNode):
              raise ConstructorError(None, None,
                      "expected a scalar node, but found %s" % node.id,
                      node.start_mark)
          return node.value
  
      def construct_sequence(self, node, deep=False):
          if not isinstance(node, SequenceNode):
              raise ConstructorError(None, None,
                      "expected a sequence node, but found %s" % node.id,
                      node.start_mark)
          return [self.construct_object(child, deep=deep)
                  for child in node.value]
  
      def construct_mapping(self, node, deep=False):
          if not isinstance(node, MappingNode):
              raise ConstructorError(None, None,
                      "expected a mapping node, but found %s" % node.id,
                      node.start_mark)
          mapping = {}
          for key_node, value_node in node.value:
              key = self.construct_object(key_node, deep=deep)
              if not isinstance(key, collections.abc.Hashable):
                  raise ConstructorError("while constructing a mapping", node.start_mark,
                          "found unhashable key", key_node.start_mark)
              value = self.construct_object(value_node, deep=deep)
              mapping[key] = value
          return mapping
  
      def construct_pairs(self, node, deep=False):
          if not isinstance(node, MappingNode):
              raise ConstructorError(None, None,
                      "expected a mapping node, but found %s" % node.id,
                      node.start_mark)
          pairs = []
          for key_node, value_node in node.value:
              key = self.construct_object(key_node, deep=deep)
              value = self.construct_object(value_node, deep=deep)
              pairs.append((key, value))
          return pairs
  
      @classmethod
      def add_constructor(cls, tag, constructor):
          if not 'yaml_constructors' in cls.__dict__:
              cls.yaml_constructors = cls.yaml_constructors.copy()
          cls.yaml_constructors[tag] = constructor
  
      @classmethod
      def add_multi_constructor(cls, tag_prefix, multi_constructor):
          if not 'yaml_multi_constructors' in cls.__dict__:
              cls.yaml_multi_constructors = cls.yaml_multi_constructors.copy()
          cls.yaml_multi_constructors[tag_prefix] = multi_constructor
  
  class SafeConstructor(BaseConstructor):
  
      def construct_scalar(self, node):
          if isinstance(node, MappingNode):
              for key_node, value_node in node.value:
                  if key_node.tag == 'tag:yaml.org,2002:value':
                      return self.construct_scalar(value_node)
          return super().construct_scalar(node)
  
      def flatten_mapping(self, node):
          merge = []
          index = 0
          while index < len(node.value):
              key_node, value_node = node.value[index]
              if key_node.tag == 'tag:yaml.org,2002:merge':
                  del node.value[index]
                  if isinstance(value_node, MappingNode):
                      self.flatten_mapping(value_node)
                      merge.extend(value_node.value)
                  elif isinstance(value_node, SequenceNode):
                      submerge = []
                      for subnode in value_node.value:
                          if not isinstance(subnode, MappingNode):
                              raise ConstructorError("while constructing a mapping",
                                      node.start_mark,
                                      "expected a mapping for merging, but found %s"
                                      % subnode.id, subnode.start_mark)
                          self.flatten_mapping(subnode)
                          submerge.append(subnode.value)
                      submerge.reverse()
                      for value in submerge:
                          merge.extend(value)
                  else:
                      raise ConstructorError("while constructing a mapping", node.start_mark,
                              "expected a mapping or list of mappings for merging, but found %s"
                              % value_node.id, value_node.start_mark)
              elif key_node.tag == 'tag:yaml.org,2002:value':
                  key_node.tag = 'tag:yaml.org,2002:str'
                  index += 1
              else:
                  index += 1
          if merge:
              node.value = merge + node.value
  
      def construct_mapping(self, node, deep=False):
          if isinstance(node, MappingNode):
              self.flatten_mapping(node)
          return super().construct_mapping(node, deep=deep)
  
      def construct_yaml_null(self, node):
          self.construct_scalar(node)
          return None
  
      bool_values = {
          'yes':      True,
          'no':       False,
          'true':     True,
          'false':    False,
          'on':       True,
          'off':      False,
      }
  
      def construct_yaml_bool(self, node):
          value = self.construct_scalar(node)
          return self.bool_values[value.lower()]
  
      def construct_yaml_int(self, node):
          value = self.construct_scalar(node)
          value = value.replace('_', '')
          sign = +1
          if value[0] == '-':
              sign = -1
          if value[0] in '+-':
              value = value[1:]
          if value == '0':
              return 0
          elif value.startswith('0b'):
              return sign*int(value[2:], 2)
          elif value.startswith('0x'):
              return sign*int(value[2:], 16)
          elif value[0] == '0':
              return sign*int(value, 8)
          elif ':' in value:
              digits = [int(part) for part in value.split(':')]
              digits.reverse()
              base = 1
              value = 0
              for digit in digits:
                  value += digit*base
                  base *= 60
              return sign*value
          else:
              return sign*int(value)
  
      inf_value = 1e300
      while inf_value != inf_value*inf_value:
          inf_value *= inf_value
      nan_value = -inf_value/inf_value   # Trying to make a quiet NaN (like C99).
  
      def construct_yaml_float(self, node):
          value = self.construct_scalar(node)
          value = value.replace('_', '').lower()
          sign = +1
          if value[0] == '-':
              sign = -1
          if value[0] in '+-':
              value = value[1:]
          if value == '.inf':
              return sign*self.inf_value
          elif value == '.nan':
              return self.nan_value
          elif ':' in value:
              digits = [float(part) for part in value.split(':')]
              digits.reverse()
              base = 1
              value = 0.0
              for digit in digits:
                  value += digit*base
                  base *= 60
              return sign*value
          else:
              return sign*float(value)
  
      def construct_yaml_binary(self, node):
          try:
              value = self.construct_scalar(node).encode('ascii')
          except UnicodeEncodeError as exc:
              raise ConstructorError(None, None,
                      "failed to convert base64 data into ascii: %s" % exc,
                      node.start_mark)
          try:
              if hasattr(base64, 'decodebytes'):
                  return base64.decodebytes(value)
              else:
                  return base64.decodestring(value)
          except binascii.Error as exc:
              raise ConstructorError(None, None,
                      "failed to decode base64 data: %s" % exc, node.start_mark)
  
      timestamp_regexp = re.compile(
              r'''^(?P<year>[0-9][0-9][0-9][0-9])
                  -(?P<month>[0-9][0-9]?)
                  -(?P<day>[0-9][0-9]?)
                  (?:(?:[Tt]|[ \t]+)
                  (?P<hour>[0-9][0-9]?)
                  :(?P<minute>[0-9][0-9])
                  :(?P<second>[0-9][0-9])
                  (?:\.(?P<fraction>[0-9]*))?
                  (?:[ \t]*(?P<tz>Z|(?P<tz_sign>[-+])(?P<tz_hour>[0-9][0-9]?)
                  (?::(?P<tz_minute>[0-9][0-9]))?))?)?$''', re.X)
  
      def construct_yaml_timestamp(self, node):
          value = self.construct_scalar(node)
          match = self.timestamp_regexp.match(node.value)
          values = match.groupdict()
          year = int(values['year'])
          month = int(values['month'])
          day = int(values['day'])
          if not values['hour']:
              return datetime.date(year, month, day)
          hour = int(values['hour'])
          minute = int(values['minute'])
          second = int(values['second'])
          fraction = 0
          if values['fraction']:
              fraction = values['fraction'][:6]
              while len(fraction) < 6:
                  fraction += '0'
              fraction = int(fraction)
          delta = None
          if values['tz_sign']:
              tz_hour = int(values['tz_hour'])
              tz_minute = int(values['tz_minute'] or 0)
              delta = datetime.timedelta(hours=tz_hour, minutes=tz_minute)
              if values['tz_sign'] == '-':
                  delta = -delta
          data = datetime.datetime(year, month, day, hour, minute, second, fraction)
          if delta:
              data -= delta
          return data
  
      def construct_yaml_omap(self, node):
          # Note: we do not check for duplicate keys, because it's too
          # CPU-expensive.
          omap = []
          yield omap
          if not isinstance(node, SequenceNode):
              raise ConstructorError("while constructing an ordered map", node.start_mark,
                      "expected a sequence, but found %s" % node.id, node.start_mark)
          for subnode in node.value:
              if not isinstance(subnode, MappingNode):
                  raise ConstructorError("while constructing an ordered map", node.start_mark,
                          "expected a mapping of length 1, but found %s" % subnode.id,
                          subnode.start_mark)
              if len(subnode.value) != 1:
                  raise ConstructorError("while constructing an ordered map", node.start_mark,
                          "expected a single mapping item, but found %d items" % len(subnode.value),
                          subnode.start_mark)
              key_node, value_node = subnode.value[0]
              key = self.construct_object(key_node)
              value = self.construct_object(value_node)
              omap.append((key, value))
  
      def construct_yaml_pairs(self, node):
          # Note: the same code as `construct_yaml_omap`.
          pairs = []
          yield pairs
          if not isinstance(node, SequenceNode):
              raise ConstructorError("while constructing pairs", node.start_mark,
                      "expected a sequence, but found %s" % node.id, node.start_mark)
          for subnode in node.value:
              if not isinstance(subnode, MappingNode):
                  raise ConstructorError("while constructing pairs", node.start_mark,
                          "expected a mapping of length 1, but found %s" % subnode.id,
                          subnode.start_mark)
              if len(subnode.value) != 1:
                  raise ConstructorError("while constructing pairs", node.start_mark,
                          "expected a single mapping item, but found %d items" % len(subnode.value),
                          subnode.start_mark)
              key_node, value_node = subnode.value[0]
              key = self.construct_object(key_node)
              value = self.construct_object(value_node)
              pairs.append((key, value))
  
      def construct_yaml_set(self, node):
          data = set()
          yield data
          value = self.construct_mapping(node)
          data.update(value)
  
      def construct_yaml_str(self, node):
          return self.construct_scalar(node)
  
      def construct_yaml_seq(self, node):
          data = []
          yield data
          data.extend(self.construct_sequence(node))
  
      def construct_yaml_map(self, node):
          data = {}
          yield data
          value = self.construct_mapping(node)
          data.update(value)
  
      def construct_yaml_object(self, node, cls):
          data = cls.__new__(cls)
          yield data
          if hasattr(data, '__setstate__'):
              state = self.construct_mapping(node, deep=True)
              data.__setstate__(state)
          else:
              state = self.construct_mapping(node)
              data.__dict__.update(state)
  
      def construct_undefined(self, node):
          raise ConstructorError(None, None,
                  "could not determine a constructor for the tag %r" % node.tag,
                  node.start_mark)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:null',
          SafeConstructor.construct_yaml_null)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:bool',
          SafeConstructor.construct_yaml_bool)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:int',
          SafeConstructor.construct_yaml_int)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:float',
          SafeConstructor.construct_yaml_float)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:binary',
          SafeConstructor.construct_yaml_binary)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:timestamp',
          SafeConstructor.construct_yaml_timestamp)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:omap',
          SafeConstructor.construct_yaml_omap)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:pairs',
          SafeConstructor.construct_yaml_pairs)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:set',
          SafeConstructor.construct_yaml_set)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:str',
          SafeConstructor.construct_yaml_str)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:seq',
          SafeConstructor.construct_yaml_seq)
  
  SafeConstructor.add_constructor(
          'tag:yaml.org,2002:map',
          SafeConstructor.construct_yaml_map)
  
  SafeConstructor.add_constructor(None,
          SafeConstructor.construct_undefined)
  
  class Constructor(SafeConstructor):
  
      def construct_python_str(self, node):
          return self.construct_scalar(node)
  
      def construct_python_unicode(self, node):
          return self.construct_scalar(node)
  
      def construct_python_bytes(self, node):
          try:
              value = self.construct_scalar(node).encode('ascii')
          except UnicodeEncodeError as exc:
              raise ConstructorError(None, None,
                      "failed to convert base64 data into ascii: %s" % exc,
                      node.start_mark)
          try:
              if hasattr(base64, 'decodebytes'):
                  return base64.decodebytes(value)
              else:
                  return base64.decodestring(value)
          except binascii.Error as exc:
              raise ConstructorError(None, None,
                      "failed to decode base64 data: %s" % exc, node.start_mark)
  
      def construct_python_long(self, node):
          return self.construct_yaml_int(node)
  
      def construct_python_complex(self, node):
         return complex(self.construct_scalar(node))
  
      def construct_python_tuple(self, node):
          return tuple(self.construct_sequence(node))
  
      def find_python_module(self, name, mark):
          if not name:
              raise ConstructorError("while constructing a Python module", mark,
                      "expected non-empty name appended to the tag", mark)
          try:
              __import__(name)
          except ImportError as exc:
              raise ConstructorError("while constructing a Python module", mark,
                      "cannot find module %r (%s)" % (name, exc), mark)
          return sys.modules[name]
  
      def find_python_name(self, name, mark):
          if not name:
              raise ConstructorError("while constructing a Python object", mark,
                      "expected non-empty name appended to the tag", mark)
          if '.' in name:
              module_name, object_name = name.rsplit('.', 1)
          else:
              module_name = 'builtins'
              object_name = name
          try:
              __import__(module_name)
          except ImportError as exc:
              raise ConstructorError("while constructing a Python object", mark,
                      "cannot find module %r (%s)" % (module_name, exc), mark)
          module = sys.modules[module_name]
          if not hasattr(module, object_name):
              raise ConstructorError("while constructing a Python object", mark,
                      "cannot find %r in the module %r"
                      % (object_name, module.__name__), mark)
          return getattr(module, object_name)
  
      def construct_python_name(self, suffix, node):
          value = self.construct_scalar(node)
          if value:
              raise ConstructorError("while constructing a Python name", node.start_mark,
                      "expected the empty value, but found %r" % value, node.start_mark)
          return self.find_python_name(suffix, node.start_mark)
  
      def construct_python_module(self, suffix, node):
          value = self.construct_scalar(node)
          if value:
              raise ConstructorError("while constructing a Python module", node.start_mark,
                      "expected the empty value, but found %r" % value, node.start_mark)
          return self.find_python_module(suffix, node.start_mark)
  
      def make_python_instance(self, suffix, node,
              args=None, kwds=None, newobj=False):
          if not args:
              args = []
          if not kwds:
              kwds = {}
          cls = self.find_python_name(suffix, node.start_mark)
          if newobj and isinstance(cls, type):
              return cls.__new__(cls, *args, **kwds)
          else:
              return cls(*args, **kwds)
  
      def set_python_instance_state(self, instance, state):
          if hasattr(instance, '__setstate__'):
              instance.__setstate__(state)
          else:
              slotstate = {}
              if isinstance(state, tuple) and len(state) == 2:
                  state, slotstate = state
              if hasattr(instance, '__dict__'):
                  instance.__dict__.update(state)
              elif state:
                  slotstate.update(state)
              for key, value in slotstate.items():
                  setattr(object, key, value)
  
      def construct_python_object(self, suffix, node):
          # Format:
          #   !!python/object:module.name { ... state ... }
          instance = self.make_python_instance(suffix, node, newobj=True)
          yield instance
          deep = hasattr(instance, '__setstate__')
          state = self.construct_mapping(node, deep=deep)
          self.set_python_instance_state(instance, state)
  
      def construct_python_object_apply(self, suffix, node, newobj=False):
          # Format:
          #   !!python/object/apply       # (or !!python/object/new)
          #   args: [ ... arguments ... ]
          #   kwds: { ... keywords ... }
          #   state: ... state ...
          #   listitems: [ ... listitems ... ]
          #   dictitems: { ... dictitems ... }
          # or short format:
          #   !!python/object/apply [ ... arguments ... ]
          # The difference between !!python/object/apply and !!python/object/new
          # is how an object is created, check make_python_instance for details.
          if isinstance(node, SequenceNode):
              args = self.construct_sequence(node, deep=True)
              kwds = {}
              state = {}
              listitems = []
              dictitems = {}
          else:
              value = self.construct_mapping(node, deep=True)
              args = value.get('args', [])
              kwds = value.get('kwds', {})
              state = value.get('state', {})
              listitems = value.get('listitems', [])
              dictitems = value.get('dictitems', {})
          instance = self.make_python_instance(suffix, node, args, kwds, newobj)
          if state:
              self.set_python_instance_state(instance, state)
          if listitems:
              instance.extend(listitems)
          if dictitems:
              for key in dictitems:
                  instance[key] = dictitems[key]
          return instance
  
      def construct_python_object_new(self, suffix, node):
          return self.construct_python_object_apply(suffix, node, newobj=True)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/none',
      Constructor.construct_yaml_null)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/bool',
      Constructor.construct_yaml_bool)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/str',
      Constructor.construct_python_str)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/unicode',
      Constructor.construct_python_unicode)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/bytes',
      Constructor.construct_python_bytes)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/int',
      Constructor.construct_yaml_int)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/long',
      Constructor.construct_python_long)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/float',
      Constructor.construct_yaml_float)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/complex',
      Constructor.construct_python_complex)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/list',
      Constructor.construct_yaml_seq)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/tuple',
      Constructor.construct_python_tuple)
  
  Constructor.add_constructor(
      'tag:yaml.org,2002:python/dict',
      Constructor.construct_yaml_map)
  
  Constructor.add_multi_constructor(
      'tag:yaml.org,2002:python/name:',
      Constructor.construct_python_name)
  
  Constructor.add_multi_constructor(
      'tag:yaml.org,2002:python/module:',
      Constructor.construct_python_module)
  
  Constructor.add_multi_constructor(
      'tag:yaml.org,2002:python/object:',
      Constructor.construct_python_object)
  
  Constructor.add_multi_constructor(
      'tag:yaml.org,2002:python/object/apply:',
      Constructor.construct_python_object_apply)
  
  Constructor.add_multi_constructor(
      'tag:yaml.org,2002:python/object/new:',
      Constructor.construct_python_object_new)
  
  