[Python] Python fixed size array (#7529)

* feat: Added support for fixed sized arrays to python Problem: We encountered that using fixed arrays from C++ to python that python would not read those arrays correctly due to no size information being encoded in the byte array itself. Fix: Encode the sizes within the generated python file during code generation. Specfically we add GetArrayAsNumpy to the python version of table, which takes as input the length of the vector. When generating the python message files we include this length from the VectorType().fixed_length. * fix: added digit support for camel case to snake case conversion Problem: When including a number in the message name we would encounter cases where SnakeCase would not add the appropirate breaks. e.g. Int32Stamped -> int_32stamped rather than int_32_stamped. Fix: To fix this we can add the condition that we check if the current character is not lower and not a digit, that we check if the previous character was a lower or digit. If it was a lower or digit then we add the break. * fix: Array support for structures Problem: The python generated code for handling non-struct and struct vectors and arrays was inconsistent. The calls to populate the obj api was creating incorrect code. Solution: To fix this the VectorOfStruct and VectorOfNonStruct was rewritten to handle array cases and bring the two methods in line which each other. Testing: PythonTesting.sh now correctly runs and generates the code for array_test.fbs. Minor modifications were done on the test to use the new index accessor for struct arrays and the script correctly sources the location of the python code. * chore: clang format changes * Added code generated by scripts/generate_code. Modified GetArrayOfNonStruct slightly to allow for function overloading allowing the user to get a single element of an array or the whole array. * Added new_line parameter to OffsetPrefix to allow optional new lines to be added. This allows us to use the GenIndents method that automatically adds new lines instead. * Reupload of generated code from the scripts/generate_code.py * Removed new line in GetVectorAsNumpy. * Updated Array lengths to use Length methods where possible. Added fallthrough for GenTypePointer. Added digit check to CamelToSnake method. Added and modified tests for ToSnakeCase and CamelToSnake. * Added range check on the getter methods for vector and array types. Renamed == as is for python
2026-06-01 19:58:15 +00:00 · 2022-09-22 19:08:09 +01:00
parent 88046190ee
commit 413115858c
24 changed files with 293 additions and 133 deletions
--- a/python/flatbuffers/table.py
+++ b/python/flatbuffers/table.py
@@ -113,6 +113,15 @@ class Table(object):
        numpy_dtype = N.to_numpy_type(flags)
        return encode.GetVectorAsNumpy(numpy_dtype, self.Bytes, length, offset)

+    def GetArrayAsNumpy(self, flags, off, length):
+        """
+        GetArrayAsNumpy returns the array with fixed width that starts at `Vector(offset)`
+        with length `length` as a numpy array with the type specified by `flags`. The
+        array is a `view` into Bytes so modifying the returned will modify Bytes in place.
+        """
+        numpy_dtype = N.to_numpy_type(flags)
+        return encode.GetVectorAsNumpy(numpy_dtype, self.Bytes, length, off)
+
    def GetVOffsetTSlot(self, slot, d):
        """
        GetVOffsetTSlot retrieves the VOffsetT that the given vtable location
@@ -125,5 +134,5 @@ class Table(object):

        off = self.Offset(slot)
        if off == 0:
-                return d
+            return d
        return off
--- a/src/idl_gen_python.cpp
+++ b/src/idl_gen_python.cpp
@@ -83,11 +83,11 @@ class PythonGenerator : public BaseGenerator {

  // Most field accessors need to retrieve and test the field offset first,
  // this is the prefix code for that.
-  std::string OffsetPrefix(const FieldDef &field) const {
+  std::string OffsetPrefix(const FieldDef &field, bool new_line = true) const {
    return "\n" + Indent + Indent +
           "o = flatbuffers.number_types.UOffsetTFlags.py_type" +
           "(self._tab.Offset(" + NumToString(field.value.offset) + "))\n" +
-           Indent + Indent + "if o != 0:\n";
+           Indent + Indent + "if o != 0:" + (new_line ? "\n" : "");
  }

  // Begin a class declaration.
@@ -164,9 +164,14 @@ class PythonGenerator : public BaseGenerator {

    GenReceiver(struct_def, code_ptr);
    code += namer_.Method(field) + "Length(self";
-    code += "):" + OffsetPrefix(field);
-    code += Indent + Indent + Indent + "return self._tab.VectorLen(o)\n";
-    code += Indent + Indent + "return 0\n\n";
+    code += "):";
+    if(!IsArray(field.value.type)){
+      code += OffsetPrefix(field,false);
+      code += GenIndents(3) + "return self._tab.VectorLen(o)";
+      code += GenIndents(2) + "return 0\n\n";
+    }else{
+      code += GenIndents(2) + "return "+NumToString(field.value.type.fixed_length)+"\n\n";
+    }
  }

  // Determines whether a vector is none or not.
@@ -177,10 +182,15 @@ class PythonGenerator : public BaseGenerator {
    GenReceiver(struct_def, code_ptr);
    code += namer_.Method(field) + "IsNone(self";
    code += "):";
-    code += GenIndents(2) +
-            "o = flatbuffers.number_types.UOffsetTFlags.py_type" +
-            "(self._tab.Offset(" + NumToString(field.value.offset) + "))";
-    code += GenIndents(2) + "return o == 0";
+    if(!IsArray(field.value.type)){
+      code += GenIndents(2) +
+              "o = flatbuffers.number_types.UOffsetTFlags.py_type" +
+              "(self._tab.Offset(" + NumToString(field.value.offset) + "))";
+      code += GenIndents(2) + "return o == 0";
+    } else {
+      //assume that we always have an array as memory is preassigned
+      code += GenIndents(2) + "return False";
+    }
    code += "\n\n";
  }

@@ -244,21 +254,42 @@ class PythonGenerator : public BaseGenerator {
    const auto vec_type = field.value.type.VectorType();
    GenReceiver(struct_def, code_ptr);
    code += namer_.Method(field);
-    if (IsStruct(vec_type)) {
-      code += "(self, obj, i):\n";
-      code += Indent + Indent + "obj.Init(self._tab.Bytes, self._tab.Pos + ";
-      code += NumToString(field.value.offset) + " + i * ";
-      code += NumToString(InlineSize(vec_type));
-      code += ")\n" + Indent + Indent + "return obj\n\n";
-    } else {
-      auto getter = GenGetter(vec_type);
-      code += "(self): return [" + getter;
-      code += "self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(";
-      code += NumToString(field.value.offset) + " + i * ";
-      code += NumToString(InlineSize(vec_type));
-      code += ")) for i in range(";
-      code += NumToString(field.value.type.fixed_length) + ")]\n";
+    code += "(self, i: int):";
+    if (parser_.opts.include_dependence_headers) {
+      code += GenIndents(2);
+      code += "from " + GenPackageReference(field.value.type) + " import " +
+              TypeName(field);
    }
+    code += GenIndents(2) + "obj = " + TypeName(field) + "()";
+    code += GenIndents(2) + "obj.Init(self._tab.Bytes, self._tab.Pos + ";
+    code += NumToString(field.value.offset) + " + i * ";
+    code += NumToString(InlineSize(vec_type));
+    code += ")" + GenIndents(2) + "return obj\n\n";
+  }
+
+  // Get the value of a vector's non-struct member. Uses a named return
+  // argument to conveniently set the zero value for the result.
+  void GetArrayOfNonStruct(const StructDef &struct_def, const FieldDef &field,
+                           std::string *code_ptr) const {
+    auto &code = *code_ptr;
+    GenReceiver(struct_def, code_ptr);
+    code += namer_.Method(field);
+    code += "(self, j = None):";
+    code += GenIndents(2) + "if j is None:";
+    code += GenIndents(3) + "return [" + GenGetter(field.value.type);
+    code += "self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(";
+    code += NumToString(field.value.offset) + " + i * ";
+    code += NumToString(InlineSize(field.value.type.VectorType()));
+    code += ")) for i in range(";
+    code += "self."+namer_.Method(field)+"Length()" + ")]";
+    code += GenIndents(2) +"elif j >= 0 and j < self."+namer_.Method(field)+"Length():";
+    code += GenIndents(3) + "return " + GenGetter(field.value.type);
+    code += "self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(";
+    code += NumToString(field.value.offset) + " + j * ";
+    code += NumToString(InlineSize(field.value.type.VectorType()));
+    code += "))";
+    code += GenIndents(2) + "else:";
+    code += GenIndents(3) + "return None\n\n";
  }

  // Get a struct by initializing an existing struct.
@@ -403,18 +434,25 @@ class PythonGenerator : public BaseGenerator {

    GenReceiver(struct_def, code_ptr);
    code += namer_.Method(field) + "AsNumpy(self):";
-    code += OffsetPrefix(field);
+    if(!IsArray(field.value.type)){
+      code += OffsetPrefix(field, false);

-    code += Indent + Indent + Indent;
-    code += "return ";
-    code += "self._tab.GetVectorAsNumpy(flatbuffers.number_types.";
-    code += namer_.Method(GenTypeGet(field.value.type));
-    code += "Flags, o)\n";
+      code += GenIndents(3);
+      code += "return ";
+      code += "self._tab.GetVectorAsNumpy(flatbuffers.number_types.";
+      code += namer_.Method(GenTypeGet(field.value.type));
+      code += "Flags, o)";

-    if (IsString(vectortype)) {
-      code += Indent + Indent + "return \"\"\n";
-    } else {
-      code += Indent + Indent + "return 0\n";
+      if (IsString(vectortype)) {
+        code += GenIndents(2) + "return \"\"\n";
+      } else {
+        code += GenIndents(2) + "return 0\n";
+      }
+    }else{
+      code += GenIndents(2) + "return ";
+      code += "self._tab.GetArrayAsNumpy(flatbuffers.number_types.";
+      code += namer_.Method(GenTypeGet(field.value.type.VectorType()));
+      code += "Flags, self._tab.Pos + "+NumToString(field.value.offset)+", "+NumToString("self."+namer_.Method(field)+"Length()")+")\n";
    }
    code += "\n";
  }
@@ -714,8 +752,6 @@ class PythonGenerator : public BaseGenerator {
      } else {
        GetScalarFieldOfTable(struct_def, field, code_ptr);
      }
-    } else if (IsArray(field.value.type)) {
-      GetArrayOfStruct(struct_def, field, code_ptr);
    } else {
      switch (field.value.type.base_type) {
        case BASE_TYPE_STRUCT:
@@ -739,6 +775,17 @@ class PythonGenerator : public BaseGenerator {
          }
          break;
        }
+        case BASE_TYPE_ARRAY: {
+          auto vectortype = field.value.type.VectorType();
+          if (vectortype.base_type == BASE_TYPE_STRUCT) {
+            GetArrayOfStruct(struct_def, field, code_ptr);
+          } else {
+            GetArrayOfNonStruct(struct_def, field, code_ptr);
+            GetVectorOfNonStructAsNumpy(struct_def, field, code_ptr);
+            GetVectorAsNestedFlatbuffer(struct_def, field, code_ptr);
+          }
+          break;
+        }
        case BASE_TYPE_UNION: GetUnionField(struct_def, field, code_ptr); break;
        default: FLATBUFFERS_ASSERT(0);
      }
@@ -1061,8 +1108,9 @@ class PythonGenerator : public BaseGenerator {

    code += GenIndents(1) + "@classmethod";
    code += GenIndents(1) + "def InitFromBuf(cls, buf, pos):";
+    code += GenIndents(2) + "n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)";
    code += GenIndents(2) + struct_var + " = " + struct_type + "()";
-    code += GenIndents(2) + struct_var + ".Init(buf, pos)";
+    code += GenIndents(2) + struct_var + ".Init(buf, pos+n)";
    code += GenIndents(2) + "return cls.InitFromObj(" + struct_var + ")";
    code += "\n";
  }
@@ -1143,12 +1191,41 @@ class PythonGenerator : public BaseGenerator {
    auto field_type = TypeName(field);
    auto one_instance = field_type + "_";
    one_instance[0] = CharToLower(one_instance[0]);
-
    if (parser_.opts.include_dependence_headers) {
      auto package_reference = GenPackageReference(field.value.type);
      field_type = package_reference + "." + TypeName(field);
    }
+    code += GenIndents(4) + "if " + struct_var + "." + field_method +
+            "(i) is None:";
+    code += GenIndents(5) + "self." + field_field + ".append(None)";
+    code += GenIndents(4) + "else:";
+    code += GenIndents(5) + one_instance + " = " + field_type +
+            "T.InitFromObj(" + struct_var + "." + field_method + "(i))";
+    code +=
+        GenIndents(5) + "self." + field_field + ".append(" + one_instance + ")";
+  }

+  void GenUnpackForTableVector(const StructDef &struct_def,
+                               const FieldDef &field,
+                               std::string *code_ptr) const {
+    auto &code = *code_ptr;
+    const auto field_field = namer_.Field(field);
+    const auto field_method = namer_.Method(field);
+    const auto struct_var = namer_.Variable(struct_def);
+
+    code += GenIndents(2) + "if not " + struct_var + "." + field_method +
+            "IsNone():";
+    code += GenIndents(3) + "self." + field_field + " = []";
+    code += GenIndents(3) + "for i in range(" + struct_var + "." +
+            field_method + "Length()):";
+
+    auto field_type = TypeName(field);
+    auto one_instance = field_type + "_";
+    one_instance[0] = CharToLower(one_instance[0]);
+    if (parser_.opts.include_dependence_headers) {
+      auto package_reference = GenPackageReference(field.value.type);
+      field_type = package_reference + "." + TypeName(field);
+    }
    code += GenIndents(4) + "if " + struct_var + "." + field_method +
            "(i) is None:";
    code += GenIndents(5) + "self." + field_field + ".append(None)";
@@ -1233,6 +1310,7 @@ class PythonGenerator : public BaseGenerator {
          GenUnPackForUnion(struct_def, field, &code);
          break;
        }
+        case BASE_TYPE_ARRAY:
        case BASE_TYPE_VECTOR: {
          auto vectortype = field.value.type.VectorType();
          if (vectortype.base_type == BASE_TYPE_STRUCT) {
@@ -1242,10 +1320,6 @@ class PythonGenerator : public BaseGenerator {
          }
          break;
        }
-        case BASE_TYPE_ARRAY: {
-          GenUnPackForScalarVector(struct_def, field, &code);
-          break;
-        }
        default: GenUnPackForScalar(struct_def, field, &code);
      }
    }
@@ -1482,6 +1556,7 @@ class PythonGenerator : public BaseGenerator {
          GenPackForUnionField(struct_def, field, &code_prefix, &code);
          break;
        }
+        case BASE_TYPE_ARRAY:
        case BASE_TYPE_VECTOR: {
          auto vectortype = field.value.type.VectorType();
          if (vectortype.base_type == BASE_TYPE_STRUCT) {
@@ -1491,10 +1566,6 @@ class PythonGenerator : public BaseGenerator {
          }
          break;
        }
-        case BASE_TYPE_ARRAY: {
-          GenPackForScalarVectorField(struct_def, field, &code_prefix, &code);
-          break;
-        }
        case BASE_TYPE_STRING: {
          code_prefix +=
              GenIndents(2) + "if self." + field_field + " is not None:";
@@ -1666,7 +1737,9 @@ class PythonGenerator : public BaseGenerator {
  std::string GenTypePointer(const Type &type) const {
    switch (type.base_type) {
      case BASE_TYPE_STRING: return "string";
-      case BASE_TYPE_VECTOR: return GenTypeGet(type.VectorType());
+      case BASE_TYPE_VECTOR:
+        // fall through
+      case BASE_TYPE_ARRAY: return GenTypeGet(type.VectorType());
      case BASE_TYPE_STRUCT: return type.struct_def->name;
      case BASE_TYPE_UNION:
        // fall through
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -109,7 +109,7 @@ static std::string ToSnakeCase(const std::string &input, bool screaming) {
    } else if (!islower(input[i])) {
      // Prevent duplicate underscores for Upper_Snake_Case strings
      // and UPPERCASE strings.
-      if (islower(input[i - 1])) { s += '_'; }
+      if (islower(input[i - 1]) || (isdigit(input[i-1]) && !isdigit(input[i]))) { s += '_'; }
      s += screaming ? CharToUpper(input[i]) : CharToLower(input[i]);
    } else {
      s += screaming ? CharToUpper(input[i]) : input[i];
@@ -135,7 +135,7 @@ std::string CamelToSnake(const std::string &input) {
    } else if (!islower(input[i])) {
      // Prevent duplicate underscores for Upper_Snake_Case strings
      // and UPPERCASE strings.
-      if (islower(input[i - 1])) { s += '_'; }
+      if (islower(input[i - 1]) || (isdigit(input[i-1]) && !isdigit(input[i]))) { s += '_'; }
      s += CharToLower(input[i]);
    } else {
      s += input[i];
--- a/tests/MyGame/Example/Ability.py
+++ b/tests/MyGame/Example/Ability.py
@@ -38,8 +38,9 @@ class AbilityT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        ability = Ability()
-        ability.Init(buf, pos)
+        ability.Init(buf, pos+n)
        return cls.InitFromObj(ability)

    @classmethod
--- a/tests/MyGame/Example/ArrayStruct.py
+++ b/tests/MyGame/Example/ArrayStruct.py
@@ -20,53 +20,65 @@ class ArrayStruct(object):
    # ArrayStruct
    def A(self): return self._tab.Get(flatbuffers.number_types.Float32Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(0))
    # ArrayStruct
-    def B(self): return [self._tab.Get(flatbuffers.number_types.Int32Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(4 + i * 4)) for i in range(15)]
+    def B(self, j = None):
+        if j is None:
+            return [self._tab.Get(flatbuffers.number_types.Int32Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(4 + i * 4)) for i in range(self.BLength())]
+        elif j >= 0 and j < self.BLength():
+            return self._tab.Get(flatbuffers.number_types.Int32Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(4 + j * 4))
+        else:
+            return None
+
+    # ArrayStruct
+    def BAsNumpy(self):
+        return self._tab.GetArrayAsNumpy(flatbuffers.number_types.Int32Flags, self._tab.Pos + 4, self.BLength())
+
    # ArrayStruct
    def BLength(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(4))
-        if o != 0:
-            return self._tab.VectorLen(o)
-        return 0
+        return 15

    # ArrayStruct
    def BIsNone(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(4))
-        return o == 0
+        return False

    # ArrayStruct
    def C(self): return self._tab.Get(flatbuffers.number_types.Int8Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(64))
    # ArrayStruct
-    def D(self, obj, i):
+    def D(self, i: int):
+        from MyGame.Example.NestedStruct import NestedStruct
+        obj = NestedStruct()
        obj.Init(self._tab.Bytes, self._tab.Pos + 72 + i * 32)
        return obj

    # ArrayStruct
    def DLength(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(72))
-        if o != 0:
-            return self._tab.VectorLen(o)
-        return 0
+        return 2

    # ArrayStruct
    def DIsNone(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(72))
-        return o == 0
+        return False

    # ArrayStruct
    def E(self): return self._tab.Get(flatbuffers.number_types.Int32Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(136))
    # ArrayStruct
-    def F(self): return [self._tab.Get(flatbuffers.number_types.Int64Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(144 + i * 8)) for i in range(2)]
+    def F(self, j = None):
+        if j is None:
+            return [self._tab.Get(flatbuffers.number_types.Int64Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(144 + i * 8)) for i in range(self.FLength())]
+        elif j >= 0 and j < self.FLength():
+            return self._tab.Get(flatbuffers.number_types.Int64Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(144 + j * 8))
+        else:
+            return None
+
+    # ArrayStruct
+    def FAsNumpy(self):
+        return self._tab.GetArrayAsNumpy(flatbuffers.number_types.Int64Flags, self._tab.Pos + 144, self.FLength())
+
    # ArrayStruct
    def FLength(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(144))
-        if o != 0:
-            return self._tab.VectorLen(o)
-        return 0
+        return 2

    # ArrayStruct
    def FIsNone(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(144))
-        return o == 0
+        return False


 def CreateArrayStruct(builder, a, b, c, d_a, d_b, d_c, d_d, e, f):
@@ -111,8 +123,9 @@ class ArrayStructT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        arrayStruct = ArrayStruct()
-        arrayStruct.Init(buf, pos)
+        arrayStruct.Init(buf, pos+n)
        return cls.InitFromObj(arrayStruct)

    @classmethod
@@ -137,7 +150,11 @@ class ArrayStructT(object):
        if not arrayStruct.DIsNone():
            self.d = []
            for i in range(arrayStruct.DLength()):
-                self.d.append(arrayStruct.D(i))
+                if arrayStruct.D(i) is None:
+                    self.d.append(None)
+                else:
+                    nestedStruct_ = MyGame.Example.NestedStruct.NestedStructT.InitFromObj(arrayStruct.D(i))
+                    self.d.append(nestedStruct_)
        self.e = arrayStruct.E()
        if not arrayStruct.FIsNone():
            if np is None:
--- a/tests/MyGame/Example/ArrayTable.py
+++ b/tests/MyGame/Example/ArrayTable.py
@@ -62,8 +62,9 @@ class ArrayTableT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        arrayTable = ArrayTable()
-        arrayTable.Init(buf, pos)
+        arrayTable.Init(buf, pos+n)
        return cls.InitFromObj(arrayTable)

    @classmethod
--- a/tests/MyGame/Example/Monster.py
+++ b/tests/MyGame/Example/Monster.py
@@ -1131,8 +1131,9 @@ class MonsterT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        monster = Monster()
-        monster.Init(buf, pos)
+        monster.Init(buf, pos+n)
        return cls.InitFromObj(monster)

    @classmethod
--- a/tests/MyGame/Example/NestedStruct.py
+++ b/tests/MyGame/Example/NestedStruct.py
@@ -18,48 +18,69 @@ class NestedStruct(object):
        self._tab = flatbuffers.table.Table(buf, pos)

    # NestedStruct
-    def A(self): return [self._tab.Get(flatbuffers.number_types.Int32Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(0 + i * 4)) for i in range(2)]
+    def A(self, j = None):
+        if j is None:
+            return [self._tab.Get(flatbuffers.number_types.Int32Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(0 + i * 4)) for i in range(self.ALength())]
+        elif j >= 0 and j < self.ALength():
+            return self._tab.Get(flatbuffers.number_types.Int32Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(0 + j * 4))
+        else:
+            return None
+
+    # NestedStruct
+    def AAsNumpy(self):
+        return self._tab.GetArrayAsNumpy(flatbuffers.number_types.Int32Flags, self._tab.Pos + 0, self.ALength())
+
    # NestedStruct
    def ALength(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(0))
-        if o != 0:
-            return self._tab.VectorLen(o)
-        return 0
+        return 2

    # NestedStruct
    def AIsNone(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(0))
-        return o == 0
+        return False

    # NestedStruct
    def B(self): return self._tab.Get(flatbuffers.number_types.Int8Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(8))
    # NestedStruct
-    def C(self): return [self._tab.Get(flatbuffers.number_types.Int8Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(9 + i * 1)) for i in range(2)]
+    def C(self, j = None):
+        if j is None:
+            return [self._tab.Get(flatbuffers.number_types.Int8Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(9 + i * 1)) for i in range(self.CLength())]
+        elif j >= 0 and j < self.CLength():
+            return self._tab.Get(flatbuffers.number_types.Int8Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(9 + j * 1))
+        else:
+            return None
+
+    # NestedStruct
+    def CAsNumpy(self):
+        return self._tab.GetArrayAsNumpy(flatbuffers.number_types.Int8Flags, self._tab.Pos + 9, self.CLength())
+
    # NestedStruct
    def CLength(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(9))
-        if o != 0:
-            return self._tab.VectorLen(o)
-        return 0
+        return 2

    # NestedStruct
    def CIsNone(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(9))
-        return o == 0
+        return False

    # NestedStruct
-    def D(self): return [self._tab.Get(flatbuffers.number_types.Int64Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(16 + i * 8)) for i in range(2)]
+    def D(self, j = None):
+        if j is None:
+            return [self._tab.Get(flatbuffers.number_types.Int64Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(16 + i * 8)) for i in range(self.DLength())]
+        elif j >= 0 and j < self.DLength():
+            return self._tab.Get(flatbuffers.number_types.Int64Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(16 + j * 8))
+        else:
+            return None
+
+    # NestedStruct
+    def DAsNumpy(self):
+        return self._tab.GetArrayAsNumpy(flatbuffers.number_types.Int64Flags, self._tab.Pos + 16, self.DLength())
+
    # NestedStruct
    def DLength(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(16))
-        if o != 0:
-            return self._tab.VectorLen(o)
-        return 0
+        return 2

    # NestedStruct
    def DIsNone(self):
-        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(16))
-        return o == 0
+        return False


 def CreateNestedStruct(builder, a, b, c, d):
@@ -90,8 +111,9 @@ class NestedStructT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        nestedStruct = NestedStruct()
-        nestedStruct.Init(buf, pos)
+        nestedStruct.Init(buf, pos+n)
        return cls.InitFromObj(nestedStruct)

    @classmethod
--- a/tests/MyGame/Example/Referrable.py
+++ b/tests/MyGame/Example/Referrable.py
@@ -53,8 +53,9 @@ class ReferrableT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        referrable = Referrable()
-        referrable.Init(buf, pos)
+        referrable.Init(buf, pos+n)
        return cls.InitFromObj(referrable)

    @classmethod
--- a/tests/MyGame/Example/Stat.py
+++ b/tests/MyGame/Example/Stat.py
@@ -75,8 +75,9 @@ class StatT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        stat = Stat()
-        stat.Init(buf, pos)
+        stat.Init(buf, pos+n)
        return cls.InitFromObj(stat)

    @classmethod
--- a/tests/MyGame/Example/StructOfStructs.py
+++ b/tests/MyGame/Example/StructOfStructs.py
@@ -64,8 +64,9 @@ class StructOfStructsT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        structOfStructs = StructOfStructs()
-        structOfStructs.Init(buf, pos)
+        structOfStructs.Init(buf, pos+n)
        return cls.InitFromObj(structOfStructs)

    @classmethod
--- a/tests/MyGame/Example/StructOfStructsOfStructs.py
+++ b/tests/MyGame/Example/StructOfStructsOfStructs.py
@@ -52,8 +52,9 @@ class StructOfStructsOfStructsT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        structOfStructsOfStructs = StructOfStructsOfStructs()
-        structOfStructsOfStructs.Init(buf, pos)
+        structOfStructsOfStructs.Init(buf, pos+n)
        return cls.InitFromObj(structOfStructsOfStructs)

    @classmethod
--- a/tests/MyGame/Example/Test.py
+++ b/tests/MyGame/Example/Test.py
@@ -39,8 +39,9 @@ class TestT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        test = Test()
-        test.Init(buf, pos)
+        test.Init(buf, pos+n)
        return cls.InitFromObj(test)

    @classmethod
--- a/tests/MyGame/Example/TestSimpleTableWithEnum.py
+++ b/tests/MyGame/Example/TestSimpleTableWithEnum.py
@@ -53,8 +53,9 @@ class TestSimpleTableWithEnumT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        testSimpleTableWithEnum = TestSimpleTableWithEnum()
-        testSimpleTableWithEnum.Init(buf, pos)
+        testSimpleTableWithEnum.Init(buf, pos+n)
        return cls.InitFromObj(testSimpleTableWithEnum)

    @classmethod
--- a/tests/MyGame/Example/TypeAliases.py
+++ b/tests/MyGame/Example/TypeAliases.py
@@ -224,8 +224,9 @@ class TypeAliasesT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        typeAliases = TypeAliases()
-        typeAliases.Init(buf, pos)
+        typeAliases.Init(buf, pos+n)
        return cls.InitFromObj(typeAliases)

    @classmethod
--- a/tests/MyGame/Example/Vec3.py
+++ b/tests/MyGame/Example/Vec3.py
@@ -68,8 +68,9 @@ class Vec3T(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        vec3 = Vec3()
-        vec3.Init(buf, pos)
+        vec3.Init(buf, pos+n)
        return cls.InitFromObj(vec3)

    @classmethod
--- a/tests/MyGame/Example2/Monster.py
+++ b/tests/MyGame/Example2/Monster.py
@@ -43,8 +43,9 @@ class MonsterT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        monster = Monster()
-        monster.Init(buf, pos)
+        monster.Init(buf, pos+n)
        return cls.InitFromObj(monster)

    @classmethod
--- a/tests/MyGame/InParentNamespace.py
+++ b/tests/MyGame/InParentNamespace.py
@@ -43,8 +43,9 @@ class InParentNamespaceT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        inParentNamespace = InParentNamespace()
-        inParentNamespace.Init(buf, pos)
+        inParentNamespace.Init(buf, pos+n)
        return cls.InitFromObj(inParentNamespace)

    @classmethod
--- a/tests/MyGame/MonsterExtra.py
+++ b/tests/MyGame/MonsterExtra.py
@@ -202,8 +202,9 @@ class MonsterExtraT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        monsterExtra = MonsterExtra()
-        monsterExtra.Init(buf, pos)
+        monsterExtra.Init(buf, pos+n)
        return cls.InitFromObj(monsterExtra)

    @classmethod
--- a/tests/PythonTest.sh
+++ b/tests/PythonTest.sh
@@ -17,12 +17,13 @@
 pushd "$(dirname $0)" >/dev/null
 test_dir="$(pwd)"
 gen_code_path=${test_dir}
-runtime_library_dir=${test_dir}/../python
+runtime_library_dir=${test_dir}/../../python

 # Emit Python code for the example schema in the test dir:
 ${test_dir}/../flatc -p -o ${gen_code_path} -I include_test monster_test.fbs --gen-object-api
 ${test_dir}/../flatc -p -o ${gen_code_path} -I include_test monster_test.fbs --gen-object-api --gen-onefile
 ${test_dir}/../flatc -p -o ${gen_code_path} -I include_test monster_extra.fbs --gen-object-api
+${test_dir}/../flatc -p -o ${gen_code_path} -I include_test arrays_test.fbs --gen-object-api

 # Syntax: run_tests <interpreter> <benchmark vtable dedupes>
 #                   <benchmark read count> <benchmark build count>
@@ -73,7 +74,7 @@ if $(which coverage >/dev/null); then

  PYTHONDONTWRITEBYTECODE=1 \
  PYTHONPATH=${runtime_library_dir}:${gen_code_path} \
-  coverage run --source=flatbuffers,MyGame py_test.py 0 0 0 > /dev/null
+  coverage run --source=flatbuffers,MyGame py_test.py 0 0 0 false > /dev/null

  echo
  cov_result=`coverage report --omit="*flatbuffers/vendor*,*py_test*" \
--- a/tests/monster_test_generated.py
+++ b/tests/monster_test_generated.py
@@ -120,8 +120,9 @@ class InParentNamespaceT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        inParentNamespace = InParentNamespace()
-        inParentNamespace.Init(buf, pos)
+        inParentNamespace.Init(buf, pos+n)
        return cls.InitFromObj(inParentNamespace)

    @classmethod
@@ -176,8 +177,9 @@ class MonsterT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        monster = Monster()
-        monster.Init(buf, pos)
+        monster.Init(buf, pos+n)
        return cls.InitFromObj(monster)

    @classmethod
@@ -231,8 +233,9 @@ class TestT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        test = Test()
-        test.Init(buf, pos)
+        test.Init(buf, pos+n)
        return cls.InitFromObj(test)

    @classmethod
@@ -295,8 +298,9 @@ class TestSimpleTableWithEnumT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        testSimpleTableWithEnum = TestSimpleTableWithEnum()
-        testSimpleTableWithEnum.Init(buf, pos)
+        testSimpleTableWithEnum.Init(buf, pos+n)
        return cls.InitFromObj(testSimpleTableWithEnum)

    @classmethod
@@ -380,8 +384,9 @@ class Vec3T(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        vec3 = Vec3()
-        vec3.Init(buf, pos)
+        vec3.Init(buf, pos+n)
        return cls.InitFromObj(vec3)

    @classmethod
@@ -439,8 +444,9 @@ class AbilityT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        ability = Ability()
-        ability.Init(buf, pos)
+        ability.Init(buf, pos+n)
        return cls.InitFromObj(ability)

    @classmethod
@@ -517,8 +523,9 @@ class StructOfStructsT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        structOfStructs = StructOfStructs()
-        structOfStructs.Init(buf, pos)
+        structOfStructs.Init(buf, pos+n)
        return cls.InitFromObj(structOfStructs)

    @classmethod
@@ -588,8 +595,9 @@ class StructOfStructsOfStructsT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        structOfStructsOfStructs = StructOfStructsOfStructs()
-        structOfStructsOfStructs.Init(buf, pos)
+        structOfStructsOfStructs.Init(buf, pos+n)
        return cls.InitFromObj(structOfStructsOfStructs)

    @classmethod
@@ -670,8 +678,9 @@ class StatT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        stat = Stat()
-        stat.Init(buf, pos)
+        stat.Init(buf, pos+n)
        return cls.InitFromObj(stat)

    @classmethod
@@ -743,8 +752,9 @@ class ReferrableT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        referrable = Referrable()
-        referrable.Init(buf, pos)
+        referrable.Init(buf, pos+n)
        return cls.InitFromObj(referrable)

    @classmethod
@@ -1716,8 +1726,9 @@ class MonsterT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        monster = Monster()
-        monster.Init(buf, pos)
+        monster.Init(buf, pos+n)
        return cls.InitFromObj(monster)

    @classmethod
@@ -2353,8 +2364,9 @@ class TypeAliasesT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        typeAliases = TypeAliases()
-        typeAliases.Init(buf, pos)
+        typeAliases.Init(buf, pos+n)
        return cls.InitFromObj(typeAliases)

    @classmethod
--- a/tests/optional_scalars/ScalarStuff.py
+++ b/tests/optional_scalars/ScalarStuff.py
@@ -438,8 +438,9 @@ class ScalarStuffT(object):

    @classmethod
    def InitFromBuf(cls, buf, pos):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, 0)
        scalarStuff = ScalarStuff()
-        scalarStuff.Init(buf, pos)
+        scalarStuff.Init(buf, pos+n)
        return cls.InitFromObj(scalarStuff)

    @classmethod
--- a/tests/py_test.py
+++ b/tests/py_test.py
@@ -2642,23 +2642,26 @@ class TestFixedLengthArrays(unittest.TestCase):
    self.assertEqual(table.A().B(), \
        [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14])
    self.assertEqual(table.A().C(), 1)
-    self.assertEqual(table.A().D(nested, 0).A(), [1, 2])
-    self.assertEqual(table.A().D(nested, 1).A(), [3, 4])
-    self.assertEqual(table.A().D(nested, 0).B(), \
+    self.assertEqual(table.A().D(0).A(), [1, 2])
+    self.assertEqual(table.A().D(1).A(), [3, 4])
+    self.assertEqual(table.A().D(0).B(), \
        MyGame.Example.TestEnum.TestEnum.B)
-    self.assertEqual(table.A().D(nested, 1).B(), \
+    self.assertEqual(table.A().D(1).B(), \
        MyGame.Example.TestEnum.TestEnum.C)
-    self.assertEqual(table.A().D(nested, 0).C(), \
+    self.assertEqual(table.A().D(0).C(), \
        [MyGame.Example.TestEnum.TestEnum.A, \
         MyGame.Example.TestEnum.TestEnum.B])
-    self.assertEqual(table.A().D(nested, 1).C(), \
+    self.assertEqual(table.A().D(1).C(), \
        [MyGame.Example.TestEnum.TestEnum.C, \
         MyGame.Example.TestEnum.TestEnum.B])
-    self.assertEqual(table.A().D(nested, 0).D(), [-1, 1])
-    self.assertEqual(table.A().D(nested, 1).D(), [-2, 2])
+    self.assertEqual(table.A().D(0).D(), [-1, 1])
+    self.assertEqual(table.A().D(1).D(), [-2, 2])
    self.assertEqual(table.A().E(), 2)
    self.assertEqual(table.A().F(), [-1, 1])
-
+    self.assertEqual(table.A().D(0).D(0), -1)
+    self.assertEqual(table.A().D(0).D(1), 1)
+    self.assertEqual(table.A().D(1).D(0), -2)
+    self.assertEqual(table.A().D(1).D(1), 2)

 def CheckAgainstGoldDataGo():
  try:
--- a/tests/util_test.cpp
+++ b/tests/util_test.cpp
@@ -149,11 +149,19 @@ void UtilConvertCase() {
    cases.push_back({ flatbuffers::Case::kUpperCamel, "tHe_qUiCk_BrOwN_fOx",
                      flatbuffers::Case::kKeep, "tHe_qUiCk_BrOwN_fOx" });
    cases.push_back({ flatbuffers::Case::kLowerCamel, "theQuick12345Fox",
-                      flatbuffers::Case::kSnake, "the_quick_12345fox" });
+                      flatbuffers::Case::kSnake, "the_quick_12345_fox" });
    cases.push_back({ flatbuffers::Case::kLowerCamel, "a12b34c45",
                      flatbuffers::Case::kSnake, "a_12b_34c_45" });
    cases.push_back({ flatbuffers::Case::kLowerCamel, "a12b34c45",
                      flatbuffers::Case::kSnake2, "a12_b34_c45" });
+    cases.push_back({ flatbuffers::Case::kUpperCamel, "Int32Stamped",
+                      flatbuffers::Case::kSnake, "int_32_stamped" });
+    cases.push_back({ flatbuffers::Case::kUpperCamel, "101DogsTest",
+                      flatbuffers::Case::kSnake, "101_dogs_test" });
+    cases.push_back({ flatbuffers::Case::kUpperCamel, "Int32Stamped",
+                      flatbuffers::Case::kScreamingSnake, "INT_32_STAMPED" });
+    cases.push_back({ flatbuffers::Case::kUpperCamel, "101DogsTest",
+                      flatbuffers::Case::kScreamingSnake, "101_DOGS_TEST" });

    for (auto &test_case : cases) {
      TEST_EQ(test_case.expected_output,