Convert ExchangeResolver to static loader class

freqtrade/resolvers/exchange_resolver.py

@@ -15,9 +15,8 @@ class ExchangeResolver(IResolver):
     This class contains all the logic to load a custom exchange class
     """
 
-    __slots__ = ['exchange']
-
-    def __init__(self, exchange_name: str, config: dict, validate: bool = True) -> None:
+    @staticmethod
+    def load_exchange(exchange_name: str, config: dict, validate: bool = True) -> Exchange:
         """
         Load the custom class from config parameter
         :param config: configuration dictionary
@@ -25,17 +24,20 @@ class ExchangeResolver(IResolver):
         # Map exchange name to avoid duplicate classes for identical exchanges
         exchange_name = MAP_EXCHANGE_CHILDCLASS.get(exchange_name, exchange_name)
         exchange_name = exchange_name.title()
+        exchange = None
         try:
-            self.exchange = self._load_exchange(exchange_name, kwargs={'config': config,
-                                                                       'validate': validate})
+            exchange = ExchangeResolver._load_exchange(exchange_name,
+                                                       kwargs={'config': config,
+                                                               'validate': validate})
         except ImportError:
             logger.info(
                 f"No {exchange_name} specific subclass found. Using the generic class instead.")
-        if not hasattr(self, "exchange"):
-            self.exchange = Exchange(config, validate=validate)
+        if not exchange:
+            exchange = Exchange(config, validate=validate)
+        return exchange
 
-    def _load_exchange(
-            self, exchange_name: str, kwargs: dict) -> Exchange:
+    @staticmethod
+    def _load_exchange(exchange_name: str, kwargs: dict) -> Exchange:
         """
         Loads the specified exchange.
         Only checks for exchanges exported in freqtrade.exchanges

freqtrade/resolvers/pairlist_resolver.py

@@ -18,8 +18,6 @@ class PairListResolver(IResolver):
     This class contains all the logic to load custom PairList class
     """
 
-    __slots__ = []
-
     @staticmethod
     def load_pairlist(pairlist_name: str, exchange, pairlistmanager,
                       config: dict, pairlistconfig: dict, pairlist_pos: int) -> IPairList:
@@ -41,7 +39,6 @@ class PairListResolver(IResolver):
                                                        'pairlistconfig': pairlistconfig,
                                                        'pairlist_pos': pairlist_pos})
 
-
     @staticmethod
     def _load_pairlist(pairlist_name: str, config: dict, kwargs: dict) -> IPairList:
         """