allow wallet update to be skipped if the value is fresh enough.

Value is NOT configurable, having this wrong can result in bans on the
exchange.

freqtrade/wallets.py

@@ -2,7 +2,10 @@
 """ Wallet """
 
 import logging
-from typing import Dict, NamedTuple, Any
+from typing import Any, Dict, NamedTuple
+
+import arrow
+
 from freqtrade.exchange import Exchange
 from freqtrade.persistence import Trade
 
@@ -24,7 +27,7 @@ class Wallets:
         self._exchange = exchange
         self._wallets: Dict[str, Wallet] = {}
         self.start_cap = config['dry_run_wallet']
-
+        self._last_wallet_refresh = 0
         self.update()
 
     def get_free(self, currency) -> float:
@@ -95,12 +98,21 @@ class Wallets:
                 balances[currency].get('total', None)
             )
 
-    def update(self) -> None:
-        if self._config['dry_run']:
-            self._update_dry()
-        else:
-            self._update_live()
-        logger.info('Wallets synced.')
+    def update(self, require_update: bool = True) -> None:
+        """
+        Updates wallets from the configured version.
+        By default, updates from the exchange.
+        Update-skipping should only be used for user-invoked /balance calls, since
+        for trading operations, the latest balance is needed.
+        :param require_update: Allow skipping an update if balances were recently refreshed
+        """
+        if (require_update or (self._last_wallet_refresh + 3600 < arrow.utcnow().timestamp)):
+            if self._config['dry_run']:
+                self._update_dry()
+            else:
+                self._update_live()
+            logger.info('Wallets synced.')
+            self._last_wallet_refresh = arrow.utcnow().timestamp
 
     def get_all_balances(self) -> Dict[str, Any]:
         return self._wallets