Initial

util/singleton.py

@@ -0,0 +1,26 @@
+class Singleton(type):
+    _instances = {}
+
+    def __call__(cls, *args, **kwargs):
+        """
+        Test:
+        >>> flag = False
+        >>> class A(metaclass=Singleton):
+        ...     def __init__(self):
+        ...         global flag
+        ...         assert not flag
+        ...         flag = True
+        ...
+        >>> class B(metaclass=Singleton): pass
+        ...
+        >>> a = A();b = B();a1 = A();b1 = B()
+        >>> id(a) == id(a1) and id(b) == id(b1) and id(a) != id(b)
+        True
+
+        :param args:
+        :param kwargs:
+        :return:
+        """
+        if cls not in cls._instances:
+            cls._instances[cls] = super().__call__(*args, **kwargs)
+        return cls._instances[cls]