refactor: use metaclass for Singleton in FiatConverter

Author: xmatthias

freqtrade/rpc/fiat_convert.py

@@ -5,14 +5,14 @@
 
 import logging
 from datetime import datetime
-from typing import Any
 
 from requests.exceptions import RequestException
 
 from freqtrade.constants import SUPPORTED_FIAT, Config
 from freqtrade.mixins.logging_mixin import LoggingMixin
 from freqtrade.util import FtTTLCache
 from freqtrade.util.coin_gecko import FtCoinGeckoApi
+from freqtrade.util.singleton import SingletonMeta
 
 
 logger = logging.getLogger(__name__)
@@ -32,26 +32,16 @@
 }
 
 
-class CryptoToFiatConverter(LoggingMixin):
+class CryptoToFiatConverter(LoggingMixin, metaclass=SingletonMeta):
     """
     Main class to initiate Crypto to FIAT.
     This object contains a list of pair Crypto, FIAT
     This object is also a Singleton
     """
 
-    __instance = None
-
     _coinlistings: list[dict] = []
     _backoff: float = 0.0
 
-    def __new__(cls, *args: Any, **kwargs: Any) -> Any:
-        """
-        Singleton pattern to ensure only one instance is created.
-        """
-        if not cls.__instance:
-            cls.__instance = super().__new__(cls)
-        return cls.__instance
-
     def __init__(self, config: Config) -> None:
         # Timeout: 6h
         self._pair_price: FtTTLCache = FtTTLCache(maxsize=500, ttl=6 * 60 * 60)

freqtrade/util/singleton.py

@@ -0,0 +1,16 @@
+from typing import Any
+
+
+class SingletonMeta(type):
+    """
+    A thread-safe implementation of Singleton.
+    Use as metaclass to create singleton classes.
+    """
+
+    _instances: dict = {}
+
+    def __call__(cls, *args: Any, **kwargs: Any) -> Any:
+        if cls not in cls._instances:
+            instance = super().__call__(*args, **kwargs)
+            cls._instances[cls] = instance
+        return cls._instances[cls]

tests/rpc/test_fiat_convert.py

@@ -12,6 +12,12 @@
 from tests.conftest import log_has, log_has_re
 
 
+@pytest.fixture(autouse=True)
+def reset_singleton_instance():
+    # Reset the singleton instance before each test
+    CryptoToFiatConverter._instances = {}
+
+
 def test_fiat_convert_is_singleton():
     fiat_convert = CryptoToFiatConverter({"a": 22})
     fiat_convert2 = CryptoToFiatConverter({})