Convert CryptoToFiatConverter into a Singleton

Result in a speed up of the unittest from 60s to 4s

Because it cost time to load Pymarketcap() every time we create
a CryptoToFiatConverter, it worth it to change it into a
Singleton.

freqtrade/fiat_convert.py

@@ -48,7 +48,10 @@ class CryptoFiat():
         return self._expiration - time.time() <= 0
 
 
-class CryptoToFiatConverter():
+class CryptoToFiatConverter(object):
+    __instance = None
+    _coinmarketcap = None
+
     # Constants
     SUPPORTED_FIAT = [
         "AUD", "BRL", "CAD", "CHF", "CLP", "CNY", "CZK", "DKK",
@@ -57,12 +60,16 @@ class CryptoToFiatConverter():
         "RUB", "SEK", "SGD", "THB", "TRY", "TWD", "ZAR", "USD"
     ]
 
-    def __init__(self) -> None:
-        try:
-            self._coinmarketcap = Pymarketcap()
-        except BaseException:
-            self._coinmarketcap = None
+    def __new__(cls):
+        if CryptoToFiatConverter.__instance is None:
+            CryptoToFiatConverter.__instance = object.__new__(cls)
+            try:
+                CryptoToFiatConverter._coinmarketcap = Pymarketcap()
+            except BaseException:
+                CryptoToFiatConverter._coinmarketcap = None
+        return CryptoToFiatConverter.__instance
 
+    def __init__(self) -> None:
         self._pairs = []
 
     def convert_amount(self, crypto_amount: float, crypto_symbol: str, fiat_symbol: str) -> float:

freqtrade/tests/rpc/test_rpc_telegram.py

@@ -219,9 +219,7 @@ def test_forcesell_handle(default_conf, update, ticker, ticker_sell_up, mocker):
     mocker.patch.multiple('freqtrade.main.exchange',
                           validate_pairs=MagicMock(),
                           get_ticker=ticker)
-    mocker.patch.multiple('freqtrade.fiat_convert.Pymarketcap',
-                          ticker=MagicMock(return_value={'price_usd': 15000.0}),
-                          _cache_symbols=MagicMock(return_value={'BTC': 1}))
+    mocker.patch('freqtrade.fiat_convert.CryptoToFiatConverter._find_price', return_value=15000.0)
     init(default_conf, create_engine('sqlite://'))
 
     # Create some test data
@@ -256,9 +254,7 @@ def test_forcesell_down_handle(default_conf, update, ticker, ticker_sell_down, m
     mocker.patch.multiple('freqtrade.main.exchange',
                           validate_pairs=MagicMock(),
                           get_ticker=ticker)
-    mocker.patch.multiple('freqtrade.fiat_convert.Pymarketcap',
-                          ticker=MagicMock(return_value={'price_usd': 15000.0}),
-                          _cache_symbols=MagicMock(return_value={'BTC': 1}))
+    mocker.patch('freqtrade.fiat_convert.CryptoToFiatConverter._find_price', return_value=15000.0)
     init(default_conf, create_engine('sqlite://'))
 
     # Create some test data
@@ -317,9 +313,7 @@ def test_forcesell_all_handle(default_conf, update, ticker, mocker):
     mocker.patch.multiple('freqtrade.main.exchange',
                           validate_pairs=MagicMock(),
                           get_ticker=ticker)
-    mocker.patch.multiple('freqtrade.fiat_convert.Pymarketcap',
-                          ticker=MagicMock(return_value={'price_usd': 15000.0}),
-                          _cache_symbols=MagicMock(return_value={'BTC': 1}))
+    mocker.patch('freqtrade.fiat_convert.CryptoToFiatConverter._find_price', return_value=15000.0)
     init(default_conf, create_engine('sqlite://'))
 
     # Create some test data

freqtrade/tests/test_fiat_convert.py

@@ -116,9 +116,9 @@ def test_fiat_convert_get_price(mocker):
     assert fiat_convert._pairs[0]._expiration is not expiration
 
 
-def test_fiat_convert_without_network(mocker):
-    pymarketcap = MagicMock(side_effect=ImportError('Oh boy, you have no network!'))
-    mocker.patch('freqtrade.fiat_convert.Pymarketcap', pymarketcap)
+def test_fiat_convert_without_network():
+    # Because CryptoToFiatConverter is a Singleton we reset the value of _coinmarketcap
+    CryptoToFiatConverter._coinmarketcap = None
 
     fiat_convert = CryptoToFiatConverter()
     assert fiat_convert._coinmarketcap is None

freqtrade/tests/test_main.py

@@ -525,9 +525,7 @@ def test_execute_sell_up(default_conf, ticker, ticker_sell_up, mocker):
     mocker.patch.multiple('freqtrade.main.exchange',
                           validate_pairs=MagicMock(),
                           get_ticker=ticker)
-    mocker.patch.multiple('freqtrade.fiat_convert.Pymarketcap',
-                          ticker=MagicMock(return_value={'price_usd': 15000.0}),
-                          _cache_symbols=MagicMock(return_value={'BTC': 1}))
+    mocker.patch('freqtrade.fiat_convert.CryptoToFiatConverter._find_price', return_value=15000.0)
     init(default_conf, create_engine('sqlite://'))
 
     # Create some test data
@@ -562,9 +560,7 @@ def test_execute_sell_down(default_conf, ticker, ticker_sell_down, mocker):
     mocker.patch.multiple('freqtrade.main.exchange',
                           validate_pairs=MagicMock(),
                           get_ticker=ticker)
-    mocker.patch.multiple('freqtrade.fiat_convert.Pymarketcap',
-                          ticker=MagicMock(return_value={'price_usd': 15000.0}),
-                          _cache_symbols=MagicMock(return_value={'BTC': 1}))
+    mocker.patch('freqtrade.fiat_convert.CryptoToFiatConverter._find_price', return_value=15000.0)
     init(default_conf, create_engine('sqlite://'))
 
     # Create some test data