Implement flexbuffers in python (#5880)

1 files changed, 1527 insertions, 0 deletions

diff --git a/python/flatbuffers/flexbuffers.py b/python/flatbuffers/flexbuffers.py
new file mode 100644
index 00000000..da10668a
--- /dev/null
+++ b/python/flatbuffers/flexbuffers.py
@@ -0,0 +1,1527 @@
+# Lint as: python3
+# Copyright 2020 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Implementation of FlexBuffers binary format.
+
+For more info check https://google.github.io/flatbuffers/flexbuffers.html and
+corresponding C++ implementation at
+https://github.com/google/flatbuffers/blob/master/include/flatbuffers/flexbuffers.h
+"""
+
+# pylint: disable=invalid-name
+# TODO(dkovalev): Add type hints everywhere, so tools like pytypes could work.
+
+import array
+import contextlib
+import enum
+import struct
+
+__all__ = ('Type', 'Builder', 'GetRoot', 'Dumps', 'Loads')
+
+
+class BitWidth(enum.IntEnum):
+  """Supported bit widths of value types.
+
+  These are used in the lower 2 bits of a type field to determine the size of
+  the elements (and or size field) of the item pointed to (e.g. vector).
+  """
+  W8 = 0  # 2^0 = 1 byte
+  W16 = 1  # 2^1 = 2 bytes
+  W32 = 2  # 2^2 = 4 bytes
+  W64 = 3  # 2^3 = 8 bytes
+
+  @staticmethod
+  def U(value):
+    """Returns the minimum `BitWidth` to encode unsigned integer value."""
+    assert value >= 0
+
+    if value < (1 << 8):
+      return BitWidth.W8
+    elif value < (1 << 16):
+      return BitWidth.W16
+    elif value < (1 << 32):
+      return BitWidth.W32
+    elif value < (1 << 64):
+      return BitWidth.W64
+    else:
+      raise ValueError('value is too big to encode: %s' % value)
+
+  @staticmethod
+  def I(value):
+    """Returns the minimum `BitWidth` to encode signed integer value."""
+    # -2^(n-1) <=     value < 2^(n-1)
+    # -2^n     <= 2 * value < 2^n
+    # 2 * value < 2^n, when value >= 0 or 2 * (-value) <= 2^n, when value < 0
+    # 2 * value < 2^n, when value >= 0 or 2 * (-value) - 1 < 2^n, when value < 0
+    #
+    # if value >= 0:
+    #   return BitWidth.U(2 * value)
+    # else:
+    #   return BitWidth.U(2 * (-value) - 1)  # ~x = -x - 1
+    value *= 2
+    return BitWidth.U(value if value >= 0 else ~value)
+
+  @staticmethod
+  def F(value):
+    """Returns the `BitWidth` to encode floating point value."""
+    if struct.unpack('f', struct.pack('f', value))[0] == value:
+      return BitWidth.W32
+    return BitWidth.W64
+
+  @staticmethod
+  def B(byte_width):
+    return {
+        1: BitWidth.W8,
+        2: BitWidth.W16,
+        4: BitWidth.W32,
+        8: BitWidth.W64
+    }[byte_width]
+
+
+I = {1: 'b', 2: 'h', 4: 'i', 8: 'q'}  # Integer formats
+U = {1: 'B', 2: 'H', 4: 'I', 8: 'Q'}  # Unsigned integer formats
+F = {4: 'f', 8: 'd'}  # Floating point formats
+
+
+def _Unpack(fmt, buf):
+  return struct.unpack(fmt[len(buf)], buf)[0]
+
+
+def _UnpackVector(fmt, buf, length):
+  byte_width = len(buf) // length
+  return struct.unpack('%d%s' % (length, fmt[byte_width]), buf)
+
+
+def _Pack(fmt, value, byte_width):
+  return struct.pack(fmt[byte_width], value)
+
+
+def _PackVector(fmt, values, byte_width):
+  return struct.pack('%d%s' % (len(values), fmt[byte_width]), *values)
+
+
+def _Mutate(fmt, buf, value, byte_width, value_bit_width):
+  if (1 << value_bit_width) <= byte_width:
+    buf[:byte_width] = _Pack(fmt, value, byte_width)
+    return True
+  return False
+
+
+# Computes how many bytes you'd have to pad to be able to write an
+# "scalar_size" scalar if the buffer had grown to "buf_size",
+# "scalar_size" is a power of two.
+def _PaddingBytes(buf_size, scalar_size):
+  # ((buf_size + (scalar_size - 1)) // scalar_size) * scalar_size - buf_size
+  return -buf_size & (scalar_size - 1)
+
+
+def _ShiftSlice(s, offset, length):
+  start = offset + (0 if s.start is None else s.start)
+  stop = offset + (length if s.stop is None else s.stop)
+  return slice(start, stop, s.step)
+
+
+# https://en.cppreference.com/w/cpp/algorithm/lower_bound
+def _LowerBound(values, value, pred):
+  """Implementation of C++ std::lower_bound() algorithm."""
+  first, last = 0, len(values)
+  count = last - first
+  while count > 0:
+    i = first
+    step = count // 2
+    i += step
+    if pred(values[i], value):
+      i += 1
+      first = i
+      count -= step + 1
+    else:
+      count = step
+  return first
+
+
+# https://en.cppreference.com/w/cpp/algorithm/binary_search
+def _BinarySearch(values, value, pred=lambda x, y: x < y):
+  """Implementation of C++ std::binary_search() algorithm."""
+  index = _LowerBound(values, value, pred)
+  if index != len(values) and not pred(value, values[index]):
+    return index
+  return -1
+
+
+class Type(enum.IntEnum):
+  """Supported types of encoded data.
+
+  These are used as the upper 6 bits of a type field to indicate the actual
+  type.
+  """
+  NULL = 0
+  INT = 1
+  UINT = 2
+  FLOAT = 3
+  # Types above stored inline, types below store an offset.
+  KEY = 4
+  STRING = 5
+  INDIRECT_INT = 6
+  INDIRECT_UINT = 7
+  INDIRECT_FLOAT = 8
+  MAP = 9
+  VECTOR = 10  # Untyped.
+
+  VECTOR_INT = 11  # Typed any size (stores no type table).
+  VECTOR_UINT = 12
+  VECTOR_FLOAT = 13
+  VECTOR_KEY = 14
+  # DEPRECATED, use VECTOR or VECTOR_KEY instead.
+  # Read test.cpp/FlexBuffersDeprecatedTest() for details on why.
+  VECTOR_STRING_DEPRECATED = 15
+
+  VECTOR_INT2 = 16  # Typed tuple (no type table, no size field).
+  VECTOR_UINT2 = 17
+  VECTOR_FLOAT2 = 18
+  VECTOR_INT3 = 19  # Typed triple (no type table, no size field).
+  VECTOR_UINT3 = 20
+  VECTOR_FLOAT3 = 21
+  VECTOR_INT4 = 22  # Typed quad (no type table, no size field).
+  VECTOR_UINT4 = 23
+  VECTOR_FLOAT4 = 24
+
+  BLOB = 25
+  BOOL = 26
+  VECTOR_BOOL = 36  # To do the same type of conversion of type to vector type
+
+  @staticmethod
+  def Pack(type_, bit_width):
+    return (int(type_) << 2) | bit_width
+
+  @staticmethod
+  def Unpack(packed_type):
+    return 1 << (packed_type & 0b11), Type(packed_type >> 2)
+
+  @staticmethod
+  def IsInline(type_):
+    return type_ <= Type.FLOAT or type_ == Type.BOOL
+
+  @staticmethod
+  def IsTypedVector(type_):
+    return Type.VECTOR_INT <= type_ <= Type.VECTOR_STRING_DEPRECATED or \
+           type_ == Type.VECTOR_BOOL
+
+  @staticmethod
+  def IsTypedVectorElementType(type_):
+    return Type.INT <= type_ <= Type.STRING or type_ == Type.BOOL
+
+  @staticmethod
+  def ToTypedVectorElementType(type_):
+    if not Type.IsTypedVector(type_):
+      raise ValueError('must be typed vector type')
+
+    return Type(type_ - Type.VECTOR_INT + Type.INT)
+
+  @staticmethod
+  def IsFixedTypedVector(type_):
+    return Type.VECTOR_INT2 <= type_ <= Type.VECTOR_FLOAT4
+
+  @staticmethod
+  def IsFixedTypedVectorElementType(type_):
+    return Type.INT <= type_ <= Type.FLOAT
+
+  @staticmethod
+  def ToFixedTypedVectorElementType(type_):
+    if not Type.IsFixedTypedVector(type_):
+      raise ValueError('must be fixed typed vector type')
+
+    # 3 types each, starting from length 2.
+    fixed_type = type_ - Type.VECTOR_INT2
+    return Type(fixed_type % 3 + Type.INT), fixed_type // 3 + 2
+
+  @staticmethod
+  def ToTypedVector(element_type, fixed_len=0):
+    """Converts element type to corresponding vector type.
+
+    Args:
+      element_type: vector element type
+      fixed_len: number of elements: 0 for typed vector; 2, 3, or 4 for fixed
+        typed vector.
+
+    Returns:
+      Typed vector type or fixed typed vector type.
+    """
+    if fixed_len == 0:
+      if not Type.IsTypedVectorElementType(element_type):
+        raise ValueError('must be typed vector element type')
+    else:
+      if not Type.IsFixedTypedVectorElementType(element_type):
+        raise ValueError('must be fixed typed vector element type')
+
+    offset = element_type - Type.INT
+    if fixed_len == 0:
+      return Type(offset + Type.VECTOR_INT)  # TypedVector
+    elif fixed_len == 2:
+      return Type(offset + Type.VECTOR_INT2)  # FixedTypedVector
+    elif fixed_len == 3:
+      return Type(offset + Type.VECTOR_INT3)  # FixedTypedVector
+    elif fixed_len == 4:
+      return Type(offset + Type.VECTOR_INT4)  # FixedTypedVector
+    else:
+      raise ValueError('unsupported fixed_len: %s' % fixed_len)
+
+
+class Buf:
+  """Class to access underlying buffer object starting from the given offset."""
+
+  def __init__(self, buf, offset):
+    self._buf = buf
+    self._offset = offset if offset >= 0 else len(buf) + offset
+    self._length = len(buf) - self._offset
+
+  def __getitem__(self, key):
+    if isinstance(key, slice):
+      return self._buf[_ShiftSlice(key, self._offset, self._length)]
+    elif isinstance(key, int):
+      return self._buf[self._offset + key]
+    else:
+      raise TypeError('invalid key type')
+
+  def __setitem__(self, key, value):
+    if isinstance(key, slice):
+      self._buf[_ShiftSlice(key, self._offset, self._length)] = value
+    elif isinstance(key, int):
+      self._buf[self._offset + key] = key
+    else:
+      raise TypeError('invalid key type')
+
+  def __repr__(self):
+    return 'buf[%d:]' % self._offset
+
+  def Find(self, sub):
+    """Returns the lowest index where the sub subsequence is found."""
+    return self._buf[self._offset:].find(sub)
+
+  def Slice(self, offset):
+    """Returns new `Buf` which starts from the given offset."""
+    return Buf(self._buf, self._offset + offset)
+
+  def Indirect(self, offset, byte_width):
+    """Return new `Buf` based on the encoded offset (indirect encoding)."""
+    return self.Slice(offset - _Unpack(U, self[offset:offset + byte_width]))
+
+
+class Object:
+  """Base class for all non-trivial data accessors."""
+  __slots__ = '_buf', '_byte_width'
+
+  def __init__(self, buf, byte_width):
+    self._buf = buf
+    self._byte_width = byte_width
+
+  @property
+  def ByteWidth(self):
+    return self._byte_width
+
+
+class Sized(Object):
+  """Base class for all data accessors which need to read encoded size."""
+  __slots__ = '_size',
+
+  def __init__(self, buf, byte_width, size=0):
+    super().__init__(buf, byte_width)
+    if size == 0:
+      self._size = _Unpack(U, self.SizeBytes)
+    else:
+      self._size = size
+
+  @property
+  def SizeBytes(self):
+    return self._buf[-self._byte_width:0]
+
+  def __len__(self):
+    return self._size
+
+
+class Blob(Sized):
+  """Data accessor for the encoded blob bytes."""
+  __slots__ = ()
+
+  @property
+  def Bytes(self):
+    return self._buf[0:len(self)]
+
+  def __repr__(self):
+    return 'Blob(%s, size=%d)' % (self._buf, len(self))
+
+
+class String(Sized):
+  """Data accessor for the encoded string bytes."""
+  __slots__ = ()
+
+  @property
+  def Bytes(self):
+    return self._buf[0:len(self)]
+
+  def Mutate(self, value):
+    """Mutates underlying string bytes in place.
+
+    Args:
+      value: New string to replace the existing one. New string must have less
+        or equal UTF-8-encoded bytes than the existing one to successfully
+        mutate underlying byte buffer.
+
+    Returns:
+      Whether the value was mutated or not.
+    """
+    encoded = value.encode('utf-8')
+    n = len(encoded)
+    if n <= len(self):
+      self._buf[-self._byte_width:0] = _Pack(U, n, self._byte_width)
+      self._buf[0:n] = encoded
+      self._buf[n:len(self)] = bytearray(len(self) - n)
+      return True
+    return False
+
+  def __str__(self):
+    return self.Bytes.decode('utf-8')
+
+  def __repr__(self):
+    return 'String(%s, size=%d)' % (self._buf, len(self))
+
+
+class Key(Object):
+  """Data accessor for the encoded key bytes."""
+  __slots__ = ()
+
+  def __init__(self, buf, byte_width):
+    assert byte_width == 1
+    super().__init__(buf, byte_width)
+
+  @property
+  def Bytes(self):
+    return self._buf[0:len(self)]
+
+  def __len__(self):
+    return self._buf.Find(0)
+
+  def __str__(self):
+    return self.Bytes.decode('ascii')
+
+  def __repr__(self):
+    return 'Key(%s, size=%d)' % (self._buf, len(self))
+
+
+class Vector(Sized):
+  """Data accessor for the encoded vector bytes."""
+  __slots__ = ()
+
+  def __getitem__(self, index):
+    if index < 0 or index >= len(self):
+      raise IndexError('vector index %s is out of [0, %d) range' % \
+          (index, len(self)))
+
+    packed_type = self._buf[len(self) * self._byte_width + index]
+    buf = self._buf.Slice(index * self._byte_width)
+    return Ref.PackedType(buf, self._byte_width, packed_type)
+
+  @property
+  def Value(self):
+    """Returns the underlying encoded data as a list object."""
+    return [e.Value for e in self]
+
+  def __repr__(self):
+    return 'Vector(%s, byte_width=%d, size=%d)' % \
+        (self._buf, self._byte_width, self._size)
+
+
+class TypedVector(Sized):
+  """Data accessor for the encoded typed vector or fixed typed vector bytes."""
+  __slots__ = '_element_type', '_size'
+
+  def __init__(self, buf, byte_width, element_type, size=0):
+    super().__init__(buf, byte_width, size)
+
+    if element_type == Type.STRING:
+      # These can't be accessed as strings, since we don't know the bit-width
+      # of the size field, see the declaration of
+      # FBT_VECTOR_STRING_DEPRECATED above for details.
+      # We change the type here to be keys, which are a subtype of strings,
+      # and will ignore the size field. This will truncate strings with
+      # embedded nulls.
+      element_type = Type.KEY
+
+    self._element_type = element_type
+
+  @property
+  def Bytes(self):
+    return self._buf[:self._byte_width * len(self)]
+
+  @property
+  def ElementType(self):
+    return self._element_type
+
+  def __getitem__(self, index):
+    if index < 0 or index >= len(self):
+      raise IndexError('vector index %s is out of [0, %d) range' % \
+          (index, len(self)))
+
+    buf = self._buf.Slice(index * self._byte_width)
+    return Ref(buf, self._byte_width, 1, self._element_type)
+
+  @property
+  def Value(self):
+    """Returns underlying data as list object."""
+    if not self:
+      return []
+
+    if self._element_type is Type.BOOL:
+      return [bool(e) for e in _UnpackVector(U, self.Bytes, len(self))]
+    elif self._element_type is Type.INT:
+      return list(_UnpackVector(I, self.Bytes, len(self)))
+    elif self._element_type is Type.UINT:
+      return list(_UnpackVector(U, self.Bytes, len(self)))
+    elif self._element_type is Type.FLOAT:
+      return list(_UnpackVector(F, self.Bytes, len(self)))
+    elif self._element_type is Type.KEY:
+      return [e.AsKey for e in self]
+    elif self._element_type is Type.STRING:
+      return [e.AsString for e in self]
+    else:
+      raise TypeError('unsupported element_type: %s' % self._element_type)
+
+  def __repr__(self):
+    return 'TypedVector(%s, byte_width=%d, element_type=%s, size=%d)' % \
+        (self._buf, self._byte_width, self._element_type, self._size)
+
+
+class Map(Vector):
+  """Data accessor for the encoded map bytes."""
+
+  @staticmethod
+  def CompareKeys(a, b):
+    if isinstance(a, Ref):
+      a = a.AsKeyBytes
+    if isinstance(b, Ref):
+      b = b.AsKeyBytes
+    return a < b
+
+  def __getitem__(self, key):
+    if isinstance(key, int):
+      return super().__getitem__(key)
+
+    index = _BinarySearch(self.Keys, key.encode('ascii'), self.CompareKeys)
+    if index != -1:
+      return super().__getitem__(index)
+
+    raise KeyError(key)
+
+  @property
+  def Keys(self):
+    byte_width = _Unpack(U, self._buf[-2 * self._byte_width:-self._byte_width])
+    buf = self._buf.Indirect(-3 * self._byte_width, self._byte_width)
+    return TypedVector(buf, byte_width, Type.KEY)
+
+  @property
+  def Values(self):
+    return Vector(self._buf, self._byte_width)
+
+  @property
+  def Value(self):
+    return {k.Value: v.Value for k, v in zip(self.Keys, self.Values)}
+
+  def __repr__(self):
+    return 'Map(%s, size=%d)' % (self._buf, len(self))
+
+
+class Ref:
+  """Data accessor for the encoded data bytes."""
+  __slots__ = '_buf', '_parent_width', '_byte_width', '_type'
+
+  @staticmethod
+  def PackedType(buf, parent_width, packed_type):
+    byte_width, type_ = Type.Unpack(packed_type)
+    return Ref(buf, parent_width, byte_width, type_)
+
+  def __init__(self, buf, parent_width, byte_width, type_):
+    self._buf = buf
+    self._parent_width = parent_width
+    self._byte_width = byte_width
+    self._type = type_
+
+  def __repr__(self):
+    return 'Ref(%s, parent_width=%d, byte_width=%d, type_=%s)' % \
+            (self._buf, self._parent_width, self._byte_width, self._type)
+
+  @property
+  def _Bytes(self):
+    return self._buf[:self._parent_width]
+
+  def _ConvertError(self, target_type):
+    raise TypeError('cannot convert %s to %s' % (self._type, target_type))
+
+  def _Indirect(self):
+    return self._buf.Indirect(0, self._parent_width)
+
+  @property
+  def IsNull(self):
+    return self._type is Type.NULL
+
+  @property
+  def IsBool(self):
+    return self._type is Type.BOOL
+
+  @property
+  def AsBool(self):
+    if self._type is Type.BOOL:
+      return bool(_Unpack(U, self._Bytes))
+    else:
+      return self.AsInt != 0
+
+  def MutateBool(self, value):
+    """Mutates underlying boolean value bytes in place.
+
+    Args:
+      value: New boolean value.
+
+    Returns:
+      Whether the value was mutated or not.
+    """
+    return self.IsBool and \
+           _Mutate(U, self._buf, value, self._parent_width, BitWidth.W8)
+
+  @property
+  def IsNumeric(self):
+    return self.IsInt or self.IsFloat
+
+  @property
+  def IsInt(self):
+    return self._type in (Type.INT, Type.INDIRECT_INT, Type.UINT,
+                          Type.INDIRECT_UINT)
+
+  @property
+  def AsInt(self):
+    """Returns current reference as integer value."""
+    if self.IsNull:
+      return 0
+    elif self.IsBool:
+      return int(self.AsBool)
+    elif self._type is Type.INT:
+      return _Unpack(I, self._Bytes)
+    elif self._type is Type.INDIRECT_INT:
+      return _Unpack(I, self._Indirect()[:self._byte_width])
+    if self._type is Type.UINT:
+      return _Unpack(U, self._Bytes)
+    elif self._type is Type.INDIRECT_UINT:
+      return _Unpack(U, self._Indirect()[:self._byte_width])
+    elif self.IsString:
+      return len(self.AsString)
+    elif self.IsKey:
+      return len(self.AsKey)
+    elif self.IsBlob:
+      return len(self.AsBlob)
+    elif self.IsVector:
+      return len(self.AsVector)
+    elif self.IsTypedVector:
+      return len(self.AsTypedVector)
+    elif self.IsFixedTypedVector:
+      return len(self.AsFixedTypedVector)
+    else:
+      raise self._ConvertError(Type.INT)
+
+  def MutateInt(self, value):
+    """Mutates underlying integer value bytes in place.
+
+    Args:
+      value: New integer value. It must fit to the byte size of the existing
+        encoded value.
+
+    Returns:
+      Whether the value was mutated or not.
+    """
+    if self._type is Type.INT:
+      return _Mutate(I, self._buf, value, self._parent_width, BitWidth.I(value))
+    elif self._type is Type.INDIRECT_INT:
+      return _Mutate(I, self._Indirect(), value, self._byte_width,
+                     BitWidth.I(value))
+    elif self._type is Type.UINT:
+      return _Mutate(U, self._buf, value, self._parent_width, BitWidth.U(value))
+    elif self._type is Type.INDIRECT_UINT:
+      return _Mutate(U, self._Indirect(), value, self._byte_width,
+                     BitWidth.U(value))
+    else:
+      return False
+
+  @property
+  def IsFloat(self):
+    return self._type in (Type.FLOAT, Type.INDIRECT_FLOAT)
+
+  @property
+  def AsFloat(self):
+    """Returns current reference as floating point value."""
+    if self.IsNull:
+      return 0.0
+    elif self.IsBool:
+      return float(self.AsBool)
+    elif self.IsInt:
+      return float(self.AsInt)
+    elif self._type is Type.FLOAT:
+      return _Unpack(F, self._Bytes)
+    elif self._type is Type.INDIRECT_FLOAT:
+      return _Unpack(F, self._Indirect()[:self._byte_width])
+    elif self.IsString:
+      return float(self.AsString)
+    elif self.IsVector:
+      return float(len(self.AsVector))
+    elif self.IsTypedVector():
+      return float(len(self.AsTypedVector))
+    elif self.IsFixedTypedVector():
+      return float(len(self.FixedTypedVector))
+    else:
+      raise self._ConvertError(Type.FLOAT)
+
+  def MutateFloat(self, value):
+    """Mutates underlying floating point value bytes in place.
+
+    Args:
+      value: New float value. It must fit to the byte size of the existing
+        encoded value.
+
+    Returns:
+      Whether the value was mutated or not.
+    """
+    if self._type is Type.FLOAT:
+      return _Mutate(F, self._buf, value, self._parent_width,
+                     BitWidth.B(self._parent_width))
+    elif self._type is Type.INDIRECT_FLOAT:
+      return _Mutate(F, self._Indirect(), value, self._byte_width,
+                     BitWidth.B(self._byte_width))
+    else:
+      return False
+
+  @property
+  def IsKey(self):
+    return self._type is Type.KEY
+
+  @property
+  def AsKeyBytes(self):
+    if self.IsKey:
+      return Key(self._Indirect(), self._byte_width).Bytes
+    else:
+      raise self._ConvertError(Type.KEY)
+
+  @property
+  def AsKey(self):
+    if self.IsKey:
+      return str(Key(self._Indirect(), self._byte_width))
+    else:
+      raise self._ConvertError(Type.KEY)
+
+  @property
+  def IsString(self):
+    return self._type is Type.STRING
+
+  @property
+  def AsString(self):
+    if self.IsString:
+      return str(String(self._Indirect(), self._byte_width))
+    elif self.IsKey:
+      return self.AsKey
+    else:
+      raise self._ConvertError(Type.STRING)
+
+  def MutateString(self, value):
+    return String(self._Indirect(), self._byte_width).Mutate(value)
+
+  @property
+  def IsBlob(self):
+    return self._type is Type.BLOB
+
+  @property
+  def AsBlob(self):
+    if self.IsBlob:
+      return Blob(self._Indirect(), self._byte_width).Bytes
+    else:
+      raise self._ConvertError(Type.BLOB)
+
+  @property
+  def IsAnyVector(self):
+    return self.IsVector or self.IsTypedVector or self.IsFixedTypedVector()
+
+  @property
+  def IsVector(self):
+    return self._type in (Type.VECTOR, Type.MAP)
+
+  @property
+  def AsVector(self):
+    if self.IsVector:
+      return Vector(self._Indirect(), self._byte_width)
+    else:
+      raise self._ConvertError(Type.VECTOR)
+
+  @property
+  def IsTypedVector(self):
+    return Type.IsTypedVector(self._type)
+
+  @property
+  def AsTypedVector(self):
+    if self.IsTypedVector:
+      return TypedVector(self._Indirect(), self._byte_width,
+                         Type.ToTypedVectorElementType(self._type))
+    else:
+      raise self._ConvertError('TYPED_VECTOR')
+
+  @property
+  def IsFixedTypedVector(self):
+    return Type.IsFixedTypedVector(self._type)
+
+  @property
+  def AsFixedTypedVector(self):
+    if self.IsFixedTypedVector:
+      element_type, size = Type.ToFixedTypedVectorElementType(self._type)
+      return TypedVector(self._Indirect(), self._byte_width, element_type, size)
+    else:
+      raise self._ConvertError('FIXED_TYPED_VECTOR')
+
+  @property
+  def IsMap(self):
+    return self._type is Type.MAP
+
+  @property
+  def AsMap(self):
+    if self.IsMap:
+      return Map(self._Indirect(), self._byte_width)
+    else:
+      raise self._ConvertError(Type.MAP)
+
+  @property
+  def Value(self):
+    """Converts current reference to value of corresponding type.
+
+    This is equivalent to calling `AsInt` for integer values, `AsFloat` for
+    floating point values, etc.
+
+    Returns:
+      Value of corresponding type.
+    """
+    if self.IsNull:
+      return None
+    elif self.IsBool:
+      return self.AsBool
+    elif self.IsInt:
+      return self.AsInt
+    elif self.IsFloat:
+      return self.AsFloat
+    elif self.IsString:
+      return self.AsString
+    elif self.IsKey:
+      return self.AsKey
+    elif self.IsBlob:
+      return self.AsBlob
+    elif self.IsMap:
+      return self.AsMap.Value
+    elif self.IsVector:
+      return self.AsVector.Value
+    elif self.IsTypedVector:
+      return self.AsTypedVector.Value
+    elif self.IsFixedTypedVector:
+      return self.AsFixedTypedVector.Value
+    else:
+      raise TypeError('cannot convert %r to value' % self)
+
+
+def _IsIterable(obj):
+  try:
+    iter(obj)
+    return True
+  except TypeError:
+    return False
+
+
+class Value:
+  """Class to represent given value during the encoding process."""
+
+  @staticmethod
+  def Null():
+    return Value(0, Type.NULL, BitWidth.W8)
+
+  @staticmethod
+  def Bool(value):
+    return Value(value, Type.BOOL, BitWidth.W8)
+
+  @staticmethod
+  def Int(value, bit_width):
+    return Value(value, Type.INT, bit_width)
+
+  @staticmethod
+  def UInt(value, bit_width):
+    return Value(value, Type.UINT, bit_width)
+
+  @staticmethod
+  def Float(value, bit_width):
+    return Value(value, Type.FLOAT, bit_width)
+
+  @staticmethod
+  def Key(offset):
+    return Value(offset, Type.KEY, BitWidth.W8)
+
+  def __init__(self, value, type_, min_bit_width):
+    self._value = value
+    self._type = type_
+
+    # For scalars: of itself, for vector: of its elements, for string: length.
+    self._min_bit_width = min_bit_width
+
+  @property
+  def Value(self):
+    return self._value
+
+  @property
+  def Type(self):
+    return self._type
+
+  @property
+  def MinBitWidth(self):
+    return self._min_bit_width
+
+  def StoredPackedType(self, parent_bit_width=BitWidth.W8):
+    return Type.Pack(self._type, self.StoredWidth(parent_bit_width))
+
+  # We have an absolute offset, but want to store a relative offset
+  # elem_index elements beyond the current buffer end. Since whether
+  # the relative offset fits in a certain byte_width depends on
+  # the size of the elements before it (and their alignment), we have
+  # to test for each size in turn.
+  def ElemWidth(self, buf_size, elem_index=0):
+    if Type.IsInline(self._type):
+      return self._min_bit_width
+    for byte_width in 1, 2, 4, 8:
+      offset_loc = buf_size + _PaddingBytes(buf_size, byte_width) + \
+                   elem_index * byte_width
+      bit_width = BitWidth.U(offset_loc - self._value)
+      if byte_width == (1 << bit_width):
+        return bit_width
+    raise ValueError('relative offset is too big')
+
+  def StoredWidth(self, parent_bit_width=BitWidth.W8):
+    if Type.IsInline(self._type):
+      return max(self._min_bit_width, parent_bit_width)
+    return self._min_bit_width
+
+  def __repr__(self):
+    return 'Value(%s, %s, %s)' % (self._value, self._type, self._min_bit_width)
+
+  def __str__(self):
+    return str(self._value)
+
+
+def InMap(func):
+  def wrapper(self, *args, **kwargs):
+    if isinstance(args[0], str):
+      self.Key(args[0])
+      func(self, *args[1:], **kwargs)
+    else:
+      func(self, *args, **kwargs)
+  return wrapper
+
+
+def InMapForString(func):
+  def wrapper(self, *args):
+    if len(args) == 1:
+      func(self, args[0])
+    elif len(args) == 2:
+      self.Key(args[0])
+      func(self, args[1])
+    else:
+      raise ValueError('invalid number of arguments')
+  return wrapper
+
+
+class Pool:
+  """Collection of (data, offset) pairs sorted by data for quick access."""
+
+  def __init__(self):
+    self._pool = []  # sorted list of (data, offset) tuples
+
+  def FindOrInsert(self, data, offset):
+    do = data, offset
+    index = _BinarySearch(self._pool, do, lambda a, b: a[0] < b[0])
+    if index != -1:
+      _, offset = self._pool[index]
+      return offset
+    self._pool.insert(index, do)
+    return None
+
+  def Clear(self):
+    self._pool = []
+
+  @property
+  def Elements(self):
+    return [data for data, _ in self._pool]
+
+
+class Builder:
+  """Helper class to encode structural data into flexbuffers format."""
+
+  def __init__(self,
+               share_strings=False,
+               share_keys=True,
+               force_min_bit_width=BitWidth.W8):
+    self._share_strings = share_strings
+    self._share_keys = share_keys
+    self._force_min_bit_width = force_min_bit_width
+
+    self._string_pool = Pool()
+    self._key_pool = Pool()
+
+    self._finished = False
+    self._buf = bytearray()
+    self._stack = []
+
+  def __len__(self):
+    return len(self._buf)
+
+  @property
+  def StringPool(self):
+    return self._string_pool
+
+  @property
+  def KeyPool(self):
+    return self._key_pool
+
+  def Clear(self):
+    self._string_pool.Clear()
+    self._key_pool.Clear()
+    self._finished = False
+    self._buf = bytearray()
+    self._stack = []
+
+  def Finish(self):
+    """Finishes encoding process and returns underlying buffer."""
+    if self._finished:
+      raise RuntimeError('builder has been already finished')
+
+    # If you hit this exception, you likely have objects that were never
+    # included in a parent. You need to have exactly one root to finish a
+    # buffer. Check your Start/End calls are matched, and all objects are inside
+    # some other object.
+    if len(self._stack) != 1:
+      raise RuntimeError('internal stack size must be one')
+
+    value = self._stack[0]
+    byte_width = self._Align(value.ElemWidth(len(self._buf)))
+    self._WriteAny(value, byte_width=byte_width)  # Root value
+    self._Write(U, value.StoredPackedType(), byte_width=1)  # Root type
+    self._Write(U, byte_width, byte_width=1)  # Root size
+
+    self.finished = True
+    return self._buf
+
+  def _ReadKey(self, offset):
+    key = self._buf[offset:]
+    return key[:key.find(0)]
+
+  def _Align(self, alignment):
+    byte_width = 1 << alignment
+    self._buf.extend(b'\x00' * _PaddingBytes(len(self._buf), byte_width))
+    return byte_width
+
+  def _Write(self, fmt, value, byte_width):
+    self._buf.extend(_Pack(fmt, value, byte_width))
+
+  def _WriteVector(self, fmt, values, byte_width):
+    self._buf.extend(_PackVector(fmt, values, byte_width))
+
+  def _WriteOffset(self, offset, byte_width):
+    relative_offset = len(self._buf) - offset
+    assert byte_width == 8 or relative_offset < (1 << (8 * byte_width))
+    self._Write(U, relative_offset, byte_width)
+
+  def _WriteAny(self, value, byte_width):
+    fmt = {
+        Type.NULL: U, Type.BOOL: U, Type.INT: I, Type.UINT: U, Type.FLOAT: F
+    }.get(value.Type)
+    if fmt:
+      self._Write(fmt, value.Value, byte_width)
+    else:
+      self._WriteOffset(value.Value, byte_width)
+
+  def _WriteBlob(self, data, append_zero, type_):
+    bit_width = BitWidth.U(len(data))
+    byte_width = self._Align(bit_width)
+    self._Write(U, len(data), byte_width)
+    loc = len(self._buf)
+    self._buf.extend(data)
+    if append_zero:
+      self._buf.append(0)
+    self._stack.append(Value(loc, type_, bit_width))
+    return loc
+
+  def _WriteScalarVector(self, element_type, byte_width, elements, fixed):
+    """Writes scalar vector elements to the underlying buffer."""
+    bit_width = BitWidth.B(byte_width)
+    # If you get this exception, you're trying to write a vector with a size
+    # field that is bigger than the scalars you're trying to write (e.g. a
+    # byte vector > 255 elements). For such types, write a "blob" instead.
+    if BitWidth.U(len(elements)) > bit_width:
+      raise ValueError('too many elements for the given byte_width')
+
+    self._Align(bit_width)
+    if not fixed:
+      self._Write(U, len(elements), byte_width)
+
+    loc = len(self._buf)
+
+    fmt = {Type.INT: I, Type.UINT: U, Type.FLOAT: F}.get(element_type)
+    if not fmt:
+      raise TypeError('unsupported element_type')
+    self._WriteVector(fmt, elements, byte_width)
+
+    type_ = Type.ToTypedVector(element_type, len(elements) if fixed else 0)
+    self._stack.append(Value(loc, type_, bit_width))
+    return loc
+
+  def _CreateVector(self, elements, typed, fixed, keys=None):
+    """Writes vector elements to the underlying buffer."""
+    length = len(elements)
+
+    if fixed and not typed:
+      raise ValueError('fixed vector must be typed')
+
+    # Figure out smallest bit width we can store this vector with.
+    bit_width = max(self._force_min_bit_width, BitWidth.U(length))
+    prefix_elems = 1  # Vector size
+    if keys:
+      bit_width = max(bit_width, keys.ElemWidth(len(self._buf)))
+      prefix_elems += 2  # Offset to the keys vector and its byte width.
+
+    vector_type = Type.KEY
+    # Check bit widths and types for all elements.
+    for i, e in enumerate(elements):
+      bit_width = max(bit_width, e.ElemWidth(len(self._buf), prefix_elems + i))
+
+      if typed:
+        if i == 0:
+          vector_type = e.Type
+        else:
+          if vector_type != e.Type:
+            raise RuntimeError('typed vector elements must be of the same type')
+
+    if fixed and not Type.IsFixedTypedVectorElementType(vector_type):
+      raise RuntimeError('must be fixed typed vector element type')
+
+    byte_width = self._Align(bit_width)
+    # Write vector. First the keys width/offset if available, and size.
+    if keys:
+      self._WriteOffset(keys.Value, byte_width)
+      self._Write(U, 1 << keys.MinBitWidth, byte_width)
+
+    if not fixed:
+      self._Write(U, length, byte_width)
+
+    # Then the actual data.
+    loc = len(self._buf)
+    for e in elements:
+      self._WriteAny(e, byte_width)
+
+    # Then the types.
+    if not typed:
+      for e in elements:
+        self._buf.append(e.StoredPackedType(bit_width))
+
+    if keys:
+      type_ = Type.MAP
+    else:
+      if typed:
+        type_ = Type.ToTypedVector(vector_type, length if fixed else 0)
+      else:
+        type_ = Type.VECTOR
+
+    return Value(loc, type_, bit_width)
+
+  def _PushIndirect(self, value, type_, bit_width):
+    byte_width = self._Align(bit_width)
+    loc = len(self._buf)
+    fmt = {
+        Type.INDIRECT_INT: I,
+        Type.INDIRECT_UINT: U,
+        Type.INDIRECT_FLOAT: F
+    }[type_]
+    self._Write(fmt, value, byte_width)
+    self._stack.append(Value(loc, type_, bit_width))
+
+  @InMapForString
+  def String(self, value):
+    """Encodes string value."""
+    reset_to = len(self._buf)
+    encoded = value.encode('utf-8')
+    loc = self._WriteBlob(encoded, append_zero=True, type_=Type.STRING)
+    if self._share_strings:
+      prev_loc = self._string_pool.FindOrInsert(encoded, loc)
+      if prev_loc is not None:
+        del self._buf[reset_to:]
+        self._stack[-1]._value = loc = prev_loc  # pylint: disable=protected-access
+
+    return loc
+
+  @InMap
+  def Blob(self, value):
+    """Encodes binary blob value.
+
+    Args:
+      value: A byte/bytearray value to encode
+
+    Returns:
+      Offset of the encoded value in underlying the byte buffer.
+    """
+    return self._WriteBlob(value, append_zero=False, type_=Type.BLOB)
+
+  def Key(self, value):
+    """Encodes key value.
+
+    Args:
+      value: A byte/bytearray/str value to encode. Byte object must not contain
+        zero bytes. String object must be convertible to ASCII.
+
+    Returns:
+      Offset of the encoded value in the underlying byte buffer.
+    """
+    if isinstance(value, (bytes, bytearray)):
+      encoded = value
+    else:
+      encoded = value.encode('ascii')
+
+    if 0 in encoded:
+      raise ValueError('key contains zero byte')
+
+    loc = len(self._buf)
+    self._buf.extend(encoded)
+    self._buf.append(0)
+    if self._share_keys:
+      prev_loc = self._key_pool.FindOrInsert(encoded, loc)
+      if prev_loc is not None:
+        del self._buf[loc:]
+        loc = prev_loc
+
+    self._stack.append(Value.Key(loc))
+    return loc
+
+  def Null(self, key=None):
+    """Encodes None value."""
+    if key:
+      self.Key(key)
+    self._stack.append(Value.Null())
+
+  @InMap
+  def Bool(self, value):
+    """Encodes boolean value.
+
+    Args:
+      value: A boolean value.
+    """
+    self._stack.append(Value.Bool(value))
+
+  @InMap
+  def Int(self, value, byte_width=0):
+    """Encodes signed integer value.
+
+    Args:
+      value: A signed integer value.
+      byte_width: Number of bytes to use: 1, 2, 4, or 8.
+    """
+    bit_width = BitWidth.I(value) if byte_width == 0 else BitWidth.B(byte_width)
+    self._stack.append(Value.Int(value, bit_width))
+
+  @InMap
+  def IndirectInt(self, value, byte_width=0):
+    """Encodes signed integer value indirectly.
+
+    Args:
+      value: A signed integer value.
+      byte_width: Number of bytes to use: 1, 2, 4, or 8.
+    """
+    bit_width = BitWidth.I(value) if byte_width == 0 else BitWidth.B(byte_width)
+    self._PushIndirect(value, Type.INDIRECT_INT, bit_width)
+
+  @InMap
+  def UInt(self, value, byte_width=0):
+    """Encodes unsigned integer value.
+
+    Args:
+      value: An unsigned integer value.
+      byte_width: Number of bytes to use: 1, 2, 4, or 8.
+    """
+    bit_width = BitWidth.U(value) if byte_width == 0 else BitWidth.B(byte_width)
+    self._stack.append(Value.UInt(value, bit_width))
+
+  @InMap
+  def IndirectUInt(self, value, byte_width=0):
+    """Encodes unsigned integer value indirectly.
+
+    Args:
+      value: An unsigned integer value.
+      byte_width: Number of bytes to use: 1, 2, 4, or 8.
+    """
+    bit_width = BitWidth.U(value) if byte_width == 0 else BitWidth.B(byte_width)
+    self._PushIndirect(value, Type.INDIRECT_UINT, bit_width)
+
+  @InMap
+  def Float(self, value, byte_width=0):
+    """Encodes floating point value.
+
+    Args:
+      value: A floating point value.
+      byte_width: Number of bytes to use: 4 or 8.
+    """
+    bit_width = BitWidth.F(value) if byte_width == 0 else BitWidth.B(byte_width)
+    self._stack.append(Value.Float(value, bit_width))
+
+  @InMap
+  def IndirectFloat(self, value, byte_width=0):
+    """Encodes floating point value indirectly.
+
+    Args:
+      value: A floating point value.
+      byte_width: Number of bytes to use: 4 or 8.
+    """
+    bit_width = BitWidth.F(value) if byte_width == 0 else BitWidth.B(byte_width)
+    self._PushIndirect(value, Type.INDIRECT_FLOAT, bit_width)
+
+  def _StartVector(self):
+    """Starts vector construction."""
+    return len(self._stack)
+
+  def _EndVector(self, start, typed, fixed):
+    """Finishes vector construction by encodung its elements."""
+    vec = self._CreateVector(self._stack[start:], typed, fixed)
+    del self._stack[start:]
+    self._stack.append(vec)
+    return vec.Value
+
+  @contextlib.contextmanager
+  def Vector(self, key=None):
+    if key:
+      self.Key(key)
+
+    try:
+      start = self._StartVector()
+      yield self
+    finally:
+      self._EndVector(start, typed=False, fixed=False)
+
+  @InMap
+  def VectorFromElements(self, elements):
+    """Encodes sequence of any elements as a vector.
+
+    Args:
+      elements: sequence of elements, they may have different types.
+    """
+    with self.Vector():
+      for e in elements:
+        self.Add(e)
+
+  @contextlib.contextmanager
+  def TypedVector(self, key=None):
+    if key:
+      self.Key(key)
+
+    try:
+      start = self._StartVector()
+      yield self
+    finally:
+      self._EndVector(start, typed=True, fixed=False)
+
+  @InMap
+  def TypedVectorFromElements(self, elements, element_type=None):
+    """Encodes sequence of elements of the same type as typed vector.
+
+    Args:
+      elements: Sequence of elements, they must be of the same type.
+      element_type: Suggested element type. Setting it to None means determining
+        correct value automatically based on the given elements.
+    """
+    if isinstance(elements, array.array):
+      if elements.typecode == 'f':
+        self._WriteScalarVector(Type.FLOAT, 4, elements, fixed=False)
+      elif elements.typecode == 'd':
+        self._WriteScalarVector(Type.FLOAT, 8, elements, fixed=False)
+      elif elements.typecode in ('b', 'h', 'i', 'l', 'q'):
+        self._WriteScalarVector(
+            Type.INT, elements.itemsize, elements, fixed=False)
+      elif elements.typecode in ('B', 'H', 'I', 'L', 'Q'):
+        self._WriteScalarVector(
+            Type.UINT, elements.itemsize, elements, fixed=False)
+      else:
+        raise ValueError('unsupported array typecode: %s' % elements.typecode)
+    else:
+      add = self.Add if element_type is None else self.Adder(element_type)
+      with self.TypedVector():
+        for e in elements:
+          add(e)
+
+  @InMap
+  def FixedTypedVectorFromElements(self,
+                                   elements,
+                                   element_type=None,
+                                   byte_width=0):
+    """Encodes sequence of elements of the same type as fixed typed vector.
+
+    Args:
+      elements: Sequence of elements, they must be of the same type. Allowed
+        types are `Type.INT`, `Type.UINT`, `Type.FLOAT`. Allowed number of
+        elements are 2, 3, or 4.
+      element_type: Suggested element type. Setting it to None means determining
+        correct value automatically based on the given elements.
+      byte_width: Number of bytes to use per element. For `Type.INT` and
+        `Type.UINT`: 1, 2, 4, or 8. For `Type.FLOAT`: 4 or 8. Setting it to 0
+        means determining correct value automatically based on the given
+        elements.
+    """
+    if not 2 <= len(elements) <= 4:
+      raise ValueError('only 2, 3, or 4 elements are supported')
+
+    types = {type(e) for e in elements}
+    if len(types) != 1:
+      raise TypeError('all elements must be of the same type')
+
+    type_, = types
+
+    if element_type is None:
+      element_type = {int: Type.INT, float: Type.FLOAT}.get(type_)
+      if not element_type:
+        raise TypeError('unsupported element_type: %s' % type_)
+
+    if byte_width == 0:
+      width = {
+          Type.UINT: BitWidth.U,
+          Type.INT: BitWidth.I,
+          Type.FLOAT: BitWidth.F
+      }[element_type]
+      byte_width = 1 << max(width(e) for e in elements)
+
+    self._WriteScalarVector(element_type, byte_width, elements, fixed=True)
+
+  def _StartMap(self):
+    """Starts map construction."""
+    return len(self._stack)
+
+  def _EndMap(self, start):
+    """Finishes map construction by encodung its elements."""
+    # Interleaved keys and values on the stack.
+    stack = self._stack[start:]
+
+    if len(stack) % 2 != 0:
+      raise RuntimeError('must be even number of keys and values')
+
+    for key in stack[::2]:
+      if key.Type is not Type.KEY:
+        raise RuntimeError('all map keys must be of %s type' % Type.KEY)
+
+    pairs = zip(stack[::2], stack[1::2])  # [(key, value), ...]
+    pairs = sorted(pairs, key=lambda pair: self._ReadKey(pair[0].Value))
+
+    del self._stack[start:]
+    for pair in pairs:
+      self._stack.extend(pair)
+
+    keys = self._CreateVector(self._stack[start::2], typed=True, fixed=False)
+    values = self._CreateVector(
+        self._stack[start + 1::2], typed=False, fixed=False, keys=keys)
+
+    del self._stack[start:]
+    self._stack.append(values)
+    return values.Value
+
+  @contextlib.contextmanager
+  def Map(self, key=None):
+    if key:
+      self.Key(key)
+
+    try:
+      start = self._StartMap()
+      yield self
+    finally:
+      self._EndMap(start)
+
+  def MapFromElements(self, elements):
+    start = self._StartMap()
+    for k, v in elements.items():
+      self.Key(k)
+      self.Add(v)
+    self._EndMap(start)
+
+  def Adder(self, type_):
+    return {
+        Type.BOOL: self.Bool,
+        Type.INT: self.Int,
+        Type.INDIRECT_INT: self.IndirectInt,
+        Type.UINT: self.UInt,
+        Type.INDIRECT_UINT: self.IndirectUInt,
+        Type.FLOAT: self.Float,
+        Type.INDIRECT_FLOAT: self.IndirectFloat,
+        Type.KEY: self.Key,
+        Type.BLOB: self.Blob,
+        Type.STRING: self.String,
+    }[type_]
+
+  @InMapForString
+  def Add(self, value):
+    """Encodes value of any supported type."""
+    if value is None:
+      self.Null()
+    elif isinstance(value, bool):
+      self.Bool(value)
+    elif isinstance(value, int):
+      self.Int(value)
+    elif isinstance(value, float):
+      self.Float(value)
+    elif isinstance(value, str):
+      self.String(value)
+    elif isinstance(value, (bytes, bytearray)):
+      self.Blob(value)
+    elif isinstance(value, dict):
+      with self.Map():
+        for k, v in value.items():
+          self.Key(k)
+          self.Add(v)
+    elif isinstance(value, array.array):
+      self.TypedVectorFromElements(value)
+    elif _IsIterable(value):
+      self.VectorFromElements(value)
+    else:
+      raise TypeError('unsupported python type: %s' % type(value))
+
+  @property
+  def LastValue(self):
+    return self._stack[-1]
+
+  @InMap
+  def ReuseValue(self, value):
+    self._stack.append(value)
+
+
+def GetRoot(buf):
+  """Returns root `Ref` object for the given buffer."""
+  if len(buf) < 3:
+    raise ValueError('buffer is too small')
+  byte_width = buf[-1]
+  return Ref.PackedType(
+      Buf(buf, -(2 + byte_width)), byte_width, packed_type=buf[-2])
+
+
+def Dumps(obj):
+  """Returns bytearray with the encoded python object."""
+  fbb = Builder()
+  fbb.Add(obj)
+  return fbb.Finish()
+
+
+def Loads(buf):
+  """Returns python object decoded from the buffer."""
+  return GetRoot(buf).Value