Added funding fee calculation methods to exchange classes

freqtrade/exchange/ftx.py

@@ -1,6 +1,6 @@
 """ FTX exchange subclass """
 import logging
-from typing import Any, Dict, List
+from typing import Any, Dict, List, Optional
 
 import ccxt
 from datetime import time
@@ -153,3 +153,21 @@ class Ftx(Exchange):
         if order['type'] == 'stop':
             return safe_value_fallback2(order, order, 'id_stop', 'id')
         return order['id']
+
+    def _get_funding_fee(
+        self,
+        contract_size: float,
+        mark_price: float,
+        funding_rate: Optional[float],
+        # index_price: float,
+        # interest_rate: float)
+    ):
+        """
+            Calculates a single funding fee
+            Always paid in USD on FTX # TODO: How do we account for this
+            :param contract_size: The amount/quanity
+            :param mark_price: The price of the asset that the contract is based off of
+            :param funding_rate: Must be None on ftx
+        """
+        (contract_size * mark_price) / 24
+        return