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Merge pull request #344 from rw/py-builder-ergonomics 

Python: Improve Builder user interface.
This commit is contained in:
Wouter van Oortmerssen 2015-11-16 09:07:31 -08:00
parent 3f1c4b41f6 3232727ace
commit f7d465f990
2 changed files with 57 additions and 36 deletions
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56
python/flatbuffers/builder.py
View File

@ -32,7 +32,7 @@ class OffsetArithmeticError(RuntimeError):
pass
class NotInObjectError(RuntimeError):
class IsNotNestedError(RuntimeError):
"""
Error caused by using a Builder to write Object data when not inside
an Object.
@ -40,7 +40,7 @@ class NotInObjectError(RuntimeError):
pass
class ObjectIsNestedError(RuntimeError):
class IsNestedError(RuntimeError):
"""
Error caused by using a Builder to begin an Object when an Object is
already being built.
@ -63,6 +63,12 @@ class BuilderSizeError(RuntimeError):
"""
pass
class BuilderNotFinishedError(RuntimeError):
"""
Error caused by not calling `Finish` before calling `Output`.
"""
pass
# VtableMetadataFields is the count of metadata fields in each vtable.
VtableMetadataFields = 2
@ -85,7 +91,7 @@ class Builder(object):
"""
__slots__ = ("Bytes", "current_vtable", "head", "minalign", "objectEnd",
"vtables")
"vtables", "nested", "finished")
"""
Maximum buffer size constant, in bytes.
@ -110,13 +116,19 @@ class Builder(object):
self.minalign = 1
self.objectEnd = None
self.vtables = []
self.nested = False
self.finished = False
def Output(self):
"""
Output returns the portion of the buffer that has been used for
writing data.
writing data. It raises BuilderNotFinishedError if the buffer has not
been finished with `Finish`.
"""
if not self.finished:
raise BuilderNotFinishedError()
return self.Bytes[self.Head():]
def StartObject(self, numfields):
@ -128,6 +140,7 @@ class Builder(object):
self.current_vtable = [0 for _ in range_func(numfields)]
self.objectEnd = self.Offset()
self.minalign = 1
self.nested = True
def WriteVtable(self):
"""
@ -236,10 +249,8 @@ class Builder(object):
def EndObject(self):
"""EndObject writes data necessary to finish object construction."""
if self.current_vtable is None:
msg = ("flatbuffers: Tried to write the end of an Object when "
"the Builder was not currently writing an Object.")
raise NotInObjectError(msg)
self.assertNested()
self.nested = False
return self.WriteVtable()
def growByteBuffer(self):
@ -336,6 +347,7 @@ class Builder(object):
"""
self.assertNotNested()
self.nested = True
self.Prep(N.Uint32Flags.bytewidth, elemSize*numElems)
self.Prep(alignment, elemSize*numElems) # In case alignment > int.
return self.Offset()
@ -343,6 +355,8 @@ class Builder(object):
def EndVector(self, vectorNumElems):
"""EndVector writes data necessary to finish vector construction."""
self.assertNested()
self.nested = False
# we already made space for this, so write without PrependUint32
self.PlaceUOffsetT(vectorNumElems)
return self.Offset()
@ -351,6 +365,7 @@ class Builder(object):
"""CreateString writes a null-terminated byte string as a vector."""
self.assertNotNested()
self.nested = True
if isinstance(s, compat.string_types):
x = s.encode()
@ -369,18 +384,24 @@ class Builder(object):
return self.EndVector(len(x))
def assertNested(self):
"""
Check that we are in the process of building an object.
"""
if not self.nested:
raise IsNotNestedError()
def assertNotNested(self):
"""
Check that no other objects are being built while making this
object. If not, raise an exception.
"""
if self.current_vtable is not None:
msg = ("flatbuffers: Tried to write a new Object when the "
"Builder was already writing an Object.")
raise ObjectIsNestedError(msg)
if self.nested:
raise IsNestedError()
def assertNested(self, obj):
def assertStructIsInline(self, obj):
"""
Structs are always stored inline, so need to be created right
where they are used. You'll get this error if you created it
@ -399,11 +420,7 @@ class Builder(object):
buffer.
"""
if self.current_vtable is None:
msg = ("flatbuffers: Tried to write an Object field when "
"the Builder was not currently writing an Object.")
raise NotInObjectError(msg)
self.assertNested()
self.current_vtable[slotnum] = self.Offset()
def Finish(self, rootTable):
@ -411,6 +428,7 @@ class Builder(object):
N.enforce_number(rootTable, N.UOffsetTFlags)
self.Prep(self.minalign, N.UOffsetTFlags.bytewidth)
self.PrependUOffsetTRelative(rootTable)
self.finished = True
return self.Head()
def Prepend(self, flags, off):
@ -470,7 +488,7 @@ class Builder(object):
N.enforce_number(d, N.UOffsetTFlags)
if x != d:
self.assertNested(x)
self.assertStructIsInline(x)
self.Slot(v)
def PrependBool(self, x): self.Prepend(N.BoolFlags, x)

37
tests/py_test.py
View File

@ -309,7 +309,7 @@ class TestByteLayout(unittest.TestCase):
want_ints = list(map(integerize, want_chars_or_ints))
want = bytearray(want_ints)
got = builder.Output()
got = builder.Bytes[builder.Head():] # use the buffer directly
self.assertEqual(want, got)
def test_numbers(self):
@ -878,24 +878,23 @@ class TestAllCodePathsOfExampleSchema(unittest.TestCase):
b = flatbuffers.Builder(0)
# make a child Monster within a vector of Monsters:
MyGame.Example.Monster.MonsterStartTestarrayoftablesVector(b, 1)
MyGame.Example.Monster.MonsterStart(b)
MyGame.Example.Monster.MonsterAddHp(b, 99)
sub_monster = MyGame.Example.Monster.MonsterEnd(b)
b.Finish(sub_monster)
tables = b.EndVector(1)
# build the vector:
MyGame.Example.Monster.MonsterStartTestarrayoftablesVector(b, 1)
b.PrependUOffsetTRelative(sub_monster)
vec = b.EndVector(1)
# make the parent monster and include the vector of Monster:
MyGame.Example.Monster.MonsterStart(b)
MyGame.Example.Monster.MonsterAddTestarrayoftables(b, tables)
MyGame.Example.Monster.MonsterAddTestarrayoftables(b, vec)
mon = MyGame.Example.Monster.MonsterEnd(b)
b.Finish(mon)
# inspect the resulting data:
mon2 = MyGame.Example.Monster.Monster.GetRootAsMonster(b.Bytes,
b.Head())
mon2 = MyGame.Example.Monster.Monster.GetRootAsMonster(b.Output(), 0)
self.assertEqual(99, mon2.Testarrayoftables(0).Hp())
self.assertEqual(1, mon2.TestarrayoftablesLength())
@ -1050,7 +1049,7 @@ class TestVtableDeduplication(unittest.TestCase):
b.PrependInt16Slot(3, 99, 0)
obj2 = b.EndObject()
got = b.Output()
got = b.Bytes[b.Head():]
want = bytearray([
240, 255, 255, 255, # == -12. offset to dedupped vtable.
@ -1107,17 +1106,16 @@ class TestVtableDeduplication(unittest.TestCase):
class TestExceptions(unittest.TestCase):
def test_not_in_object_error(self):
b = flatbuffers.Builder(0)
exc = None
assertRaises(self, lambda: b.EndObject(),
flatbuffers.builder.NotInObjectError)
def test_object_is_nested_error(self):
b = flatbuffers.Builder(0)
b.StartObject(0)
assertRaises(self, lambda: b.StartObject(0),
flatbuffers.builder.ObjectIsNestedError)
flatbuffers.builder.IsNestedError)
def test_object_is_not_nested_error(self):
b = flatbuffers.Builder(0)
assertRaises(self, lambda: b.EndObject(),
flatbuffers.builder.IsNotNestedError)
def test_struct_is_not_inline_error(self):
b = flatbuffers.Builder(0)
@ -1135,7 +1133,12 @@ class TestExceptions(unittest.TestCase):
b.StartObject(0)
s = 'test1'
assertRaises(self, lambda: b.CreateString(s),
flatbuffers.builder.ObjectIsNestedError)
flatbuffers.builder.IsNestedError)
def test_finished_bytes_error(self):
b = flatbuffers.Builder(0)
assertRaises(self, lambda: b.Output(),
flatbuffers.builder.BuilderNotFinishedError)
def CheckAgainstGoldDataGo():