Singleton Python Class Example

In order to create a Singleton class, you can override its __new__ method to return the same instance every time.

Here is an example:

class MySingletonClass:
    _instance = None
 
    def __new__(cls, *args, **kwargs):
        if cls._instance is None:
            cls._instance = super().__new__(cls, *args, **kwargs)
        return cls._instance
 
s1 = Singleton()
s2 = Singleton()
print(s1 is s2) # True

or you can use a decorator:

from functools import wraps
 
def singleton(cls):
    @wraps(cls)
    def wrapper_singleton(*args, **kwargs):
        if not wrapper_singleton.instance:
            wrapper_singleton.instance = cls(*args, **kwargs)
        return wrapper_singleton.instance
    wrapper_singleton.instance = None
    return wrapper_singleton

Usage:

@singleton
class MyClass:
    pass
 
m1 = MyClass()
m2 = MyClass()
print(m1 is m2) # True

Note: There is a wrapper_singleton.instance in the code above. This is a function attribute.

I know it’s weird, but it’s a thing in Python.

You can read more about it in the PEP proposal and this StackOverflow question.