139 lines
5.0 KiB
Python
139 lines
5.0 KiB
Python
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# Copyright 2014 Google Inc. All rights reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from . import encode
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from . import number_types as N
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class Table(object):
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"""Table wraps a byte slice and provides read access to its data.
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The variable `Pos` indicates the root of the FlatBuffers object therein."""
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__slots__ = ("Bytes", "Pos")
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def __init__(self, buf, pos):
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N.enforce_number(pos, N.UOffsetTFlags)
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self.Bytes = buf
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self.Pos = pos
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def Offset(self, vtableOffset):
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"""Offset provides access into the Table's vtable.
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Deprecated fields are ignored by checking the vtable's length."""
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vtable = self.Pos - self.Get(N.SOffsetTFlags, self.Pos)
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vtableEnd = self.Get(N.VOffsetTFlags, vtable)
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if vtableOffset < vtableEnd:
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return self.Get(N.VOffsetTFlags, vtable + vtableOffset)
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return 0
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def Indirect(self, off):
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"""Indirect retrieves the relative offset stored at `offset`."""
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N.enforce_number(off, N.UOffsetTFlags)
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return off + encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)
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def String(self, off):
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"""String gets a string from data stored inside the flatbuffer."""
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N.enforce_number(off, N.UOffsetTFlags)
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off += encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)
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start = off + N.UOffsetTFlags.bytewidth
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length = encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)
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return bytes(self.Bytes[start:start+length])
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def VectorLen(self, off):
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"""VectorLen retrieves the length of the vector whose offset is stored
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at "off" in this object."""
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N.enforce_number(off, N.UOffsetTFlags)
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off += self.Pos
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off += encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)
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ret = encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)
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return ret
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def Vector(self, off):
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"""Vector retrieves the start of data of the vector whose offset is
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stored at "off" in this object."""
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N.enforce_number(off, N.UOffsetTFlags)
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off += self.Pos
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x = off + self.Get(N.UOffsetTFlags, off)
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# data starts after metadata containing the vector length
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x += N.UOffsetTFlags.bytewidth
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return x
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def Union(self, t2, off):
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"""Union initializes any Table-derived type to point to the union at
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the given offset."""
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assert type(t2) is Table
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N.enforce_number(off, N.UOffsetTFlags)
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off += self.Pos
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t2.Pos = off + self.Get(N.UOffsetTFlags, off)
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t2.Bytes = self.Bytes
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def Get(self, flags, off):
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"""
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Get retrieves a value of the type specified by `flags` at the
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given offset.
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"""
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N.enforce_number(off, N.UOffsetTFlags)
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return flags.py_type(encode.Get(flags.packer_type, self.Bytes, off))
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def GetSlot(self, slot, d, validator_flags):
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N.enforce_number(slot, N.VOffsetTFlags)
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if validator_flags is not None:
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N.enforce_number(d, validator_flags)
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off = self.Offset(slot)
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if off == 0:
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return d
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return self.Get(validator_flags, self.Pos + off)
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def GetVectorAsNumpy(self, flags, off):
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"""
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GetVectorAsNumpy returns the vector that starts at `Vector(off)`
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as a numpy array with the type specified by `flags`. The array is
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a `view` into Bytes, so modifying the returned array will
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modify Bytes in place.
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"""
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offset = self.Vector(off)
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length = self.VectorLen(off) # TODO: length accounts for bytewidth, right?
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numpy_dtype = N.to_numpy_type(flags)
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return encode.GetVectorAsNumpy(numpy_dtype, self.Bytes, length, offset)
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def GetArrayAsNumpy(self, flags, off, length):
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"""
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GetArrayAsNumpy returns the array with fixed width that starts at `Vector(offset)`
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with length `length` as a numpy array with the type specified by `flags`. The
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array is a `view` into Bytes so modifying the returned will modify Bytes in place.
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"""
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numpy_dtype = N.to_numpy_type(flags)
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return encode.GetVectorAsNumpy(numpy_dtype, self.Bytes, length, off)
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def GetVOffsetTSlot(self, slot, d):
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"""
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GetVOffsetTSlot retrieves the VOffsetT that the given vtable location
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points to. If the vtable value is zero, the default value `d`
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will be returned.
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"""
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N.enforce_number(slot, N.VOffsetTFlags)
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N.enforce_number(d, N.VOffsetTFlags)
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off = self.Offset(slot)
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if off == 0:
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return d
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return off
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