Given two modules, main and x with the following contents:
main:
class Singleton(object):
_instance = None
def __new__(cls, *args, **kwargs):
if not cls._instance:
cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs)
cls._instance.x = 10
return cls._instance
uvw = Singleton()
if __name__ == "__main__":
print(id(uvw))
uvw.x += 10
print(uvw.x)
import x
and x, respectively:
import main
print(id(main.uvw))
print(main.uvw.x)
I would now expect that executing main would yield the same IDs and the value twenty in both instances, but what I get is this:
$ python main.py
140592861777168
20
140592861207504
10
Is there any way I can ensure that uvw
is the same object at both places?
I reckon the problem is that your Singleton
class is somehow being reloaded, and thus loses its _instance
field in the second module.
I think this will work:
singleton.py
:
class Singleton(object):
_instance = None
def __new__(cls, *args, **kwargs):
if not cls._instance:
cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs)
cls._instance.x = 10
return cls._instance
a.py
:
from singleton import Singleton
uvw = Singleton()
print(id(uvw))
uvw.x += 10
print(uvw.x)
b.py
:
from singleton import Singleton
uvw = Singleton()
print(id(uvw))
uvw.x += 10
print(uvw.x)
main.py
import a
import b
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