Decode bytes to strings in Python Object API (#8551)

include/flatbuffers/idl.h

@@ -710,6 +710,7 @@ struct IDLOptions {
   /********************************** Python **********************************/
   bool python_no_type_prefix_suffix;
   bool python_typing;
+  bool python_decode_obj_api_strings=false;
 
   // The target Python version. Can be one of the following:
   // -  "0"

scripts/generate_code.py

@@ -104,7 +104,7 @@ JAVA_OPTS = ["--java"]
 KOTLIN_OPTS = ["--kotlin"]
 PHP_OPTS = ["--php"]
 DART_OPTS = ["--dart"]
-PYTHON_OPTS = ["--python", "--python-typing"]
+PYTHON_OPTS = ["--python", "--python-typing", "--python-decode-obj-api-string"]
 BINARY_OPTS = ["-b", "--schema", "--bfbs-comments", "--bfbs-builtins"]
 PROTO_OPTS = ["--proto"]
 

src/flatc.cpp

@@ -256,6 +256,7 @@ const static FlatCOption flatc_options[] = {
     "Skip emission of Python functions that are prefixed with typenames" },
   { "", "python-typing", "", "Generate Python type annotations" },
   { "", "python-version", "", "Generate code for the given Python version." },
+  { "", "python-decode-obj-api-strings", "", "Decode bytes to strings for the Python Object API"},
   { "", "python-gen-numpy", "", "Whether to generate numpy helpers." },
   { "", "ts-omit-entrypoint", "",
     "Omit emission of namespace entrypoint file" },
@@ -682,6 +683,8 @@ FlatCOptions FlatCompiler::ParseFromCommandLineArguments(int argc,
       } else if (arg == "--python-version") {
         if (++argi >= argc) Error("missing value following: " + arg, true);
         opts.python_version = argv[argi];
+      } else if (arg == "--python-decode-obj-api-strings") {
+        opts.python_decode_obj_api_strings = true;
       } else if (arg == "--python-gen-numpy" ||
                  arg == "--python-gen-numpy=true") {
         opts.python_gen_numpy = true;

src/idl_gen_python.cpp

@@ -2028,6 +2028,20 @@ class PythonGenerator : public BaseGenerator {
     }
   }
 
+  void GenUnPackForString(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) + "self." + field_field + " = " + struct_var + "." +
+            field_method + "()";
+    code += GenIndents(2) + "if self." + field_field + " is not None:";
+    code += GenIndents(3) + "self." + field_field + " = self." + field_field +
+            ".decode('utf-8')";
+  }
+
   void GenUnPackForScalar(const StructDef &struct_def, const FieldDef &field,
                           std::string *code_ptr) const {
     auto &code = *code_ptr;
@@ -2070,6 +2084,14 @@ class PythonGenerator : public BaseGenerator {
           }
           break;
         }
+        case BASE_TYPE_STRING: {
+          if (parser_.opts.python_decode_obj_api_strings) {
+            GenUnPackForString(struct_def, field, &code);
+          } else {
+            GenUnPackForScalar(struct_def, field, &code);
+          }
+          break;
+        }
         default: GenUnPackForScalar(struct_def, field, &code);
       }
     }

tests/MyGame/Example/NestedUnion/NestedUnionTest.py

@@ -132,6 +132,8 @@ class NestedUnionTestT(object):
         if nestedUnionTest is None:
             return
         self.name = nestedUnionTest.Name()
+        if self.name is not None:
+            self.name = self.name.decode('utf-8')
         self.dataType = nestedUnionTest.DataType()
         self.data = MyGame.Example.NestedUnion.Any.AnyCreator(self.dataType, nestedUnionTest.Data())
         self.id = nestedUnionTest.Id()