Fix method name parsing in NoMethodMatchPythonExceptionInterpreter

Common/Exceptions/NoMethodMatchPythonExceptionInterpreter.cs

@@ -50,13 +50,36 @@ public override Exception Interpret(Exception exception, IExceptionInterpreter i
         {
             var pe = (PythonException)exception;
 
-            var startIndex = pe.Message.LastIndexOfInvariant(" ");
-            var methodName = pe.Message.Substring(startIndex).Trim();
+            var methodName = GetMethodName(pe.Message);
             var message = Messages.NoMethodMatchPythonExceptionInterpreter.AttemptedToAccessMethodThatDoesNotExist(methodName);
 
             message += PythonUtil.PythonExceptionStackParser(pe.StackTrace);
 
             return new MissingMethodException(message, pe);
         }
+
+        /// <summary>
+        /// Extracts the name of the method that failed to resolve from the Python exception message.
+        /// The message has the form: "No method matches given arguments for {methodName}: ({argumentTypes})",
+        /// so the method name sits between the "for " keyword and the following ":".
+        /// </summary>
+        private static string GetMethodName(string exceptionMessage)
+        {
+            const string forKeyword = "for ";
+            var forIndex = exceptionMessage.IndexOfInvariant(forKeyword);
+            if (forIndex == -1)
+            {
+                // Unexpected format, fall back to the whole message
+                return exceptionMessage.Trim();
+            }
+
+            var methodNameStart = forIndex + forKeyword.Length;
+            var colonIndex = exceptionMessage.IndexOf(':', methodNameStart);
+            var methodName = colonIndex > methodNameStart
+                ? exceptionMessage.Substring(methodNameStart, colonIndex - methodNameStart)
+                : exceptionMessage.Substring(methodNameStart);
+
+            return methodName.Trim();
+        }
     }
 }

Tests/Common/Exceptions/NoMethodMatchPythonExceptionInterpreterTests.cs

@@ -83,6 +83,42 @@ public void VerifyMessageContainsStackTraceInformation()
             Assert.True(exception.Message.Contains("self.set_cash('SPY')"));
         }
 
+        [Test]
+        public void VerifyMessageContainsTheMethodName()
+        {
+            var exception = CreateExceptionFromType(typeof(PythonException));
+            var interpreter = new NoMethodMatchPythonExceptionInterpreter();
+            exception = interpreter.Interpret(exception, NullExceptionInterpreter.Instance);
+
+            // The interpreter should reference the actual method name that failed to resolve (SetCash),
+            // not a fragment of the argument type list (e.g. "'str'>)").
+            Assert.That(exception.Message, Does.Contain("SetCash"));
+            Assert.That(exception.Message, Does.Not.Contain(">)"));
+        }
+
+        [Test]
+        public void VerifyMessageContainsTheMethodNameForOverloadedMethod()
+        {
+            PythonException pythonException;
+            using (Py.GIL())
+            {
+                var module = Py.Import("Test_PythonExceptionInterpreter");
+                dynamic algorithm = module.GetAttr("Test_PythonExceptionInterpreter").Invoke();
+
+                // self.rsi(symbol, 15, Resolution.DAILY) -- the third argument should be a
+                // MovingAverageType, so no RSI overload matches the given arguments.
+                pythonException = Assert.Throws<PythonException>(() => algorithm.no_method_match_rsi());
+            }
+
+            var interpreter = new NoMethodMatchPythonExceptionInterpreter();
+            var exception = interpreter.Interpret(pythonException, NullExceptionInterpreter.Instance);
+
+            // The interpreter should reference the RSI method name, not a fragment of the
+            // argument type list (e.g. "'QuantConnect.Resolution'>)").
+            Assert.That(exception.Message, Does.Contain("RSI"));
+            Assert.That(exception.Message, Does.Not.Contain(">)"));
+        }
+
         private Exception CreateExceptionFromType(Type type) => type == typeof(PythonException) ? _pythonException : (Exception)Activator.CreateInstance(type);
     }
 }

Tests/RegressionAlgorithms/Test_PythonExceptionInterpreter.py

@@ -23,6 +23,12 @@ def key_error(self):
     def no_method_match(self):
         self.set_cash('SPY')
 
+    def no_method_match_rsi(self):
+        symbol = Symbol.create('SPY', SecurityType.EQUITY, Market.USA)
+        # The third positional argument should be a MovingAverageType, not a Resolution,
+        # so no RSI overload matches the given arguments.
+        self._indicator = self.rsi(symbol, 15, Resolution.DAILY)
+
     def unsupported_operand(self):
         x = None + "Pepe Grillo"