Don't show None when evaluating in repl. Fixes #678

Author: fabioz

src/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_comm.py

@@ -1234,8 +1234,6 @@ def __create_frame():
             _evaluate_response(py_db, request, result='', error_message='Thread id: %s is not current thread id.' % (thread_id,))
             return
 
-    variable = frame_tracker.obtain_as_variable(expression, eval_result, frame=frame)
-
     safe_repr_custom_attrs = {}
     if context == 'clipboard':
         safe_repr_custom_attrs = dict(
@@ -1245,16 +1243,25 @@ def __create_frame():
             maxother_inner=2 ** 64,
         )
 
-    var_data = variable.get_var_data(fmt=fmt, **safe_repr_custom_attrs)
+    if context == 'repl' and eval_result is None:
+        # We don't want "None" to appear when typing in the repl.
+        body = pydevd_schema.EvaluateResponseBody(
+            result=None,
+            variablesReference=0,
+        )
 
-    body = pydevd_schema.EvaluateResponseBody(
-        result=var_data['value'],
-        variablesReference=var_data.get('variablesReference', 0),
-        type=var_data.get('type'),
-        presentationHint=var_data.get('presentationHint'),
-        namedVariables=var_data.get('namedVariables'),
-        indexedVariables=var_data.get('indexedVariables'),
-    )
+    else:
+        variable = frame_tracker.obtain_as_variable(expression, eval_result, frame=frame)
+        var_data = variable.get_var_data(fmt=fmt, **safe_repr_custom_attrs)
+
+        body = pydevd_schema.EvaluateResponseBody(
+            result=var_data['value'],
+            variablesReference=var_data.get('variablesReference', 0),
+            type=var_data.get('type'),
+            presentationHint=var_data.get('presentationHint'),
+            namedVariables=var_data.get('namedVariables'),
+            indexedVariables=var_data.get('indexedVariables'),
+        )
     variables_response = pydevd_base_schema.build_response(request, kwargs={'body':body})
     py_db.writer.add_command(NetCommand(CMD_RETURN, 0, variables_response, is_json=True))
 

src/debugpy/_vendored/pydevd/tests_python/test_debugger_json.py

@@ -504,6 +504,8 @@ def evaluate(self, expression, frameId=None, context=None, fmt=None, success=Tru
         '''
         :param wait_for_response:
             If True returns the response, otherwise returns the request.
+
+        :returns EvaluateResponse
         '''
         eval_request = self.write_request(
             pydevd_schema.EvaluateRequest(pydevd_schema.EvaluateArguments(
@@ -1926,26 +1928,25 @@ def test_evaluate_no_name_mangling(case_setup):
         json_hit = json_facade.get_stack_as_json_hit(json_hit.thread_id)
 
         # Check eval with a properly indented block
-        json_facade.evaluate(
-            'x = "_"',
-            frameId=json_hit.frame_id,
-            context="repl",
-        )
-        json_facade.evaluate(
-            'x',
-            frameId=json_hit.frame_id,
-            context="repl",
-        )
-        json_facade.evaluate(
-            'y = "__"',
-            frameId=json_hit.frame_id,
-            context="repl",
-        )
-        json_facade.evaluate(
-            'y',
-            frameId=json_hit.frame_id,
-            context="repl",
-        )
+        evaluate_response = json_facade.evaluate(
+            'x = "_"', frameId=json_hit.frame_id, context="repl")
+        assert not evaluate_response.body.result
+
+        evaluate_response = json_facade.evaluate(
+            'x', frameId=json_hit.frame_id, context="repl")
+        assert evaluate_response.body.result == "'_'"
+
+        evaluate_response = json_facade.evaluate(
+            'y = "__"', frameId=json_hit.frame_id, context="repl")
+        assert not evaluate_response.body.result
+
+        evaluate_response = json_facade.evaluate(
+            'y', frameId=json_hit.frame_id, context="repl")
+        assert evaluate_response.body.result == "'__'"
+
+        evaluate_response = json_facade.evaluate(
+            'None', json_hit.frame_id, context='repl')
+        assert not evaluate_response.body.result
 
         json_facade.write_continue()
         writer.finished_ok = True