diff --git a/alpaca_trade_api/rest.py b/alpaca_trade_api/rest.py
index 64f20c63..2255e198 100644
--- a/alpaca_trade_api/rest.py
+++ b/alpaca_trade_api/rest.py
@@ -269,10 +269,10 @@ def list_orders(self,
 
     def submit_order(self,
                      symbol: str,
-                     qty: int,
-                     side: str,
-                     type: str,
-                     time_in_force: str,
+                     qty: float = None,
+                     side: str = "buy",
+                     type: str = "market",
+                     time_in_force: str = "day",
                      limit_price: str = None,
                      stop_price: str = None,
                      client_order_id: str = None,
@@ -281,10 +281,11 @@ def submit_order(self,
                      take_profit: dict = None,
                      stop_loss: dict = None,
                      trail_price: str = None,
-                     trail_percent: str = None):
+                     trail_percent: str = None,
+                     notional: float = None):
         """
         :param symbol: symbol or asset ID
-        :param qty: int
+        :param qty: float. Mutually exclusive with "notional".
         :param side: buy or sell
         :param type: market, limit, stop, stop_limit or trailing_stop
         :param time_in_force: day, gtc, opg, cls, ioc, fok
@@ -300,15 +301,19 @@ def submit_order(self,
                {"stop_price": "297.95", "limit_price": "298.95"}
         :param trail_price: str of float
         :param trail_percent: str of float
+        :param notional: float. Mutually exclusive with "qty".
         """
         """Request a new order"""
         params = {
             'symbol':        symbol,
-            'qty':           qty,
             'side':          side,
             'type':          type,
             'time_in_force': time_in_force
         }
+        if qty is not None:
+            params['qty'] = qty
+        if notional is not None:
+            params['notional'] = notional
         if limit_price is not None:
             params['limit_price'] = FLOAT(limit_price)
         if stop_price is not None:
@@ -335,7 +340,7 @@ def submit_order(self,
             params['trail_percent'] = trail_percent
         resp = self.post('/orders', params)
         return self.response_wrapper(resp, Order)
-
+    
     def get_order_by_client_order_id(self, client_order_id: str) -> Order:
         """Get an order by client order id"""
         params = {
diff --git a/alpaca_trade_api/stream2.py b/alpaca_trade_api/stream2.py
index d56c6cb1..c3c26e06 100644
--- a/alpaca_trade_api/stream2.py
+++ b/alpaca_trade_api/stream2.py
@@ -123,6 +123,8 @@ async def _ensure_ws(self):
     async def subscribe(self, channels):
         if isinstance(channels, str):
             channels = [channels]
+        elif isinstance(channels, set):
+            channels = list(channels)
         if len(channels) > 0:
             await self._ensure_ws()
             self._streams |= set(channels)
@@ -136,6 +138,8 @@ async def subscribe(self, channels):
     async def unsubscribe(self, channels):
         if isinstance(channels, str):
             channels = [channels]
+        elif isinstance(channels, set):
+            channels = list(channels)
         if len(channels) > 0:
             await self._ws.send(json.dumps({
                 'action': 'unlisten',