[Python] (scalar) vector reading speedup via numpy (#4390)

* Add numpy accessor to python flatbuffers scalar vectors

* Update python tests to test numpy vector accessor

* Update appveyor CI to run Python tests, save generated code as artifact

* Update example generated python code

* Add numpy info to python usage docs

* Update test schema and python tests w/ multi-byte vector

* did not mean to push profiling code

* adding float64 numpy tests

1 files changed, 33 insertions, 0 deletions

diff --git a/src/idl_gen_python.cpp b/src/idl_gen_python.cpp
index c16a0117..257515b7 100644
--- a/src/idl_gen_python.cpp
+++ b/src/idl_gen_python.cpp
@@ -274,6 +274,38 @@ static void GetMemberOfVectorOfNonStruct(const StructDef &struct_def,
   code += "\n";
 }
 
+// Returns a non-struct vector as a numpy array. Much faster
+// than iterating over the vector element by element.
+static void GetVectorOfNonStructAsNumpy(const StructDef &struct_def,
+                                        const FieldDef &field,
+                                        std::string *code_ptr) {
+  std::string &code = *code_ptr;
+  auto vectortype = field.value.type.VectorType();
+
+  // Currently, we only support accessing as numpy array if
+  // the vector type is a scalar.
+  if (!(IsScalar(vectortype.base_type))) {
+    return;
+  }
+
+  GenReceiver(struct_def, code_ptr);
+  code += MakeCamel(field.name) + "AsNumpy(self):";
+  code += OffsetPrefix(field);
+
+  code += Indent + Indent + Indent;
+  code += "return ";
+  code += "self._tab.GetVectorAsNumpy(flatbuffers.number_types.";
+  code += MakeCamel(GenTypeGet(field.value.type));
+  code += "Flags, o)\n";
+
+  if (vectortype.base_type == BASE_TYPE_STRING) {
+    code += Indent + Indent + "return \"\"\n";
+  } else {
+    code += Indent + Indent + "return 0\n";
+  }
+  code += "\n";
+}
+
 // Begin the creator function signature.
 static void BeginBuilderArgs(const StructDef &struct_def,
                              std::string *code_ptr) {
@@ -440,6 +472,7 @@ static void GenStructAccessor(const StructDef &struct_def,
           GetMemberOfVectorOfStruct(struct_def, field, code_ptr);
         } else {
           GetMemberOfVectorOfNonStruct(struct_def, field, code_ptr);
+          GetVectorOfNonStructAsNumpy(struct_def, field, code_ptr);
         }
         break;
       }