calculate_funding_fees is actually a public exchange interface (used in backtesting).

freqtrade/exchange/exchange.py

@@ -1923,7 +1923,7 @@ class Exchange:
         funding_rates = candle_histories[funding_comb]
         mark_rates = candle_histories[mark_comb]
 
-        return self._calculate_funding_fees(
+        return self.calculate_funding_fees(
             funding_rates=funding_rates,
             mark_rates=mark_rates,
             amount=amount,
@@ -1931,7 +1931,7 @@ class Exchange:
             close_date=close_date
         )
 
-    def _calculate_funding_fees(
+    def calculate_funding_fees(
         self,
         funding_rates: DataFrame,
         mark_rates: DataFrame,

freqtrade/exchange/kraken.py

@@ -159,7 +159,7 @@ class Kraken(Exchange):
             params['leverage'] = leverage
         return params
 
-    def _calculate_funding_fees(
+    def calculate_funding_fees(
         self,
         funding_rates: DataFrame,
         mark_rates: DataFrame,

freqtrade/optimize/backtesting.py

@@ -488,7 +488,7 @@ class Backtesting:
         sell_candle_time: datetime = sell_row[DATE_IDX].to_pydatetime()
 
         if self.trading_mode == TradingMode.FUTURES:
-            trade.funding_fees = self.exchange._calculate_funding_fees(
+            trade.funding_fees = self.exchange.calculate_funding_fees(
                 funding_rates=self.futures_data[CandleType.FUNDING_RATE][trade.pair],
                 mark_rates=self.futures_data[CandleType.MARK][trade.pair],
                 amount=trade.amount,