Bring frame_objects.py into mypy compliance.

presubmit.py

@@ -19,6 +19,7 @@
 
 subprocess.check_call([
     'mypy',
+    'src/echo/frame_objects.py',
     'src/echo/__init__.py',
     'src/echo/import_routines.py',
     'src/echo/bc_helpers.py',

src/echo/frame_objects.py

@@ -255,6 +255,7 @@ def _handle_exception(self, why: WhyStatus,
             if (why == WhyStatus.CONTINUE and
                     self.block_stack[-1].kind == BlockKind.SETUP_LOOP):
                 b = self.block_stack[-1]
+                assert isinstance(return_value, int), return_value
                 self.pc = return_value
                 return True
 
@@ -1176,7 +1177,9 @@ def _run_one_bytecode(self) -> Optional[Result[Tuple[Value, ReturnKind]]]:
             return Result((v, ReturnKind.RETURN))
 
         if instruction.opname == 'YIELD_VALUE':
-            self.pc += self.pc_to_bc_width[self.pc]
+            yield_width: Optional[int] = self.pc_to_bc_width[self.pc]
+            assert yield_width is not None
+            self.pc += yield_width
             return Result((Value(self._peek()), ReturnKind.YIELD))
 
         f = getattr(self, '_run_{}'.format(instruction.opname))
@@ -1268,7 +1271,7 @@ def get_dict(self):
     def get_bases(self):
         raise NotImplementedError
 
-    def get_mro(self) -> Tuple[EPyObject, ...]:
+    def get_mro(self) -> Tuple[Union[EPyType, type], ...]:
         return (self,)
 
     def get_type(self) -> EPyType:

src/echo/interp_context.py

@@ -1,6 +1,7 @@
-from typing import Any, Callable
+from typing import Any, Callable, Optional
 
 from echo.interpreter_state import InterpreterState
+from echo.interp_result import ExceptionData
 
 
 EModule = Any
@@ -20,7 +21,7 @@ def __init__(self, interp_state: InterpreterState,
         interp_state.sys_modules['sys'] = esys
         self.ebuiltins = ebuiltins
         self.desc_count = 0
-        self.exc_info = None
+        self.exc_info: Optional[ExceptionData] = None
         self.call_profiler = None
 
     def call(self, *args, **kwargs):