Python singleton

class Singleton:
    """
    A non-thread-safe helper class to ease implementing singletons.
    This should be used as a decorator -- not a metaclass -- to the
    class that should be a singleton.

    The decorated class can define one `__init__` function that
    takes only the `self` argument. Also, the decorated class cannot be
    inherited from. Other than that, there are no restrictions that apply
    to the decorated class.

    To get the singleton instance, use the `instance` method. Trying
    to use `__call__` will result in a `TypeError` being raised.

    """

    def __init__(self, decorated):
        self._decorated = decorated

    def instance(self):
        """
        Returns the singleton instance. Upon its first call, it creates a
        new instance of the decorated class and calls its `__init__` method.
        On all subsequent calls, the already created instance is returned.

        """
        try:
            return self._instance
        except AttributeError:
            self._instance = self._decorated()
            return self._instance

    def __call__(self):
        raise TypeError('Singletons must be accessed through `instance()`.')

    def __instancecheck__(self, inst):
        return isinstance(inst, self._decorated)

Source: stackoverflow.com

Similar codes

3 votes168 views2 answers
Find number of vowels in string python
Python
0 vote154 views2 answers
Get random vowel python
Python
-1 vote193 views1 answer
Django cheat sheet pdf
Python Django
21 votes161 views6 answers
Pygame install
Python
0 vote158 views2 answers
Doing math in python
Python
0 vote198 views1 answer
Python simple number formatting samples
Python
0 vote170 views1 answer
Blender python set object location
Python
0 vote173 views3 answers
Print out session information django
Python
0 vote170 views1 answer
Python open dicom
Python
0 vote174 views1 answer
Python ignore unicodedecodeerror
Python