wallet: cache NaN coin prices, clear cache on new history

electrum/gui/kivy/main_window.py

@@ -173,6 +173,7 @@ class ElectrumWindow(App):
 
     def on_history(self, d):
         Logger.info("on_history")
+        self.wallet.clear_coin_price_cache()
         self._trigger_update_history()
 
     def on_fee_histogram(self, *args):

electrum/gui/qt/main_window.py

@@ -222,6 +222,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
         self.fetch_alias()
 
     def on_history(self, b):
+        self.wallet.clear_coin_price_cache()
         self.new_fx_history_signal.emit()
 
     def setup_exception_hook(self):

electrum/wallet.py

@@ -182,7 +182,7 @@ class Abstract_Wallet(AddressSynchronizer):
         self.invoices = InvoiceStore(self.storage)
         self.contacts = Contacts(self.storage)
 
-        self.coin_price_cache = {}
+        self._coin_price_cache = {}
 
     def load_and_cleanup(self):
         self.load_keystore()
@@ -1178,6 +1178,9 @@ class Abstract_Wallet(AddressSynchronizer):
                 total_price += self.coin_price(ser.split(':')[0], price_func, ccy, v)
         return total_price / (input_value/Decimal(COIN))
 
+    def clear_coin_price_cache(self):
+        self._coin_price_cache = {}
+
     def coin_price(self, txid, price_func, ccy, txin_value):
         """
         Acquisition price of a coin.
@@ -1185,17 +1188,13 @@ class Abstract_Wallet(AddressSynchronizer):
         """
         if txin_value is None:
             return Decimal('NaN')
-        # FIXME: this mutual recursion will be really slow and might even reach
-        # max recursion depth if there are no FX rates available as then
-        # nothing will be cached.
         cache_key = "{}:{}:{}".format(str(txid), str(ccy), str(txin_value))
-        result = self.coin_price_cache.get(cache_key, None)
+        result = self._coin_price_cache.get(cache_key, None)
         if result is not None:
             return result
         if self.txi.get(txid, {}) != {}:
             result = self.average_price(txid, price_func, ccy) * txin_value/Decimal(COIN)
-            if not result.is_nan():
-                self.coin_price_cache[cache_key] = result
+            self._coin_price_cache[cache_key] = result
             return result
         else:
             fiat_value = self.get_fiat_value(txid, ccy)