Show More
keyedinstance.py
36 lines
| 1.1 KiB
| text/x-python
|
PythonLexer
r1 | #!/usr/bin/env python | |||
# -*- coding: utf-8 -*- | ||||
class KeyedInstance(object): | ||||
"""A class whose instances have a unique identifier of some sort | ||||
No two instances with the same unique ID should exist - if we try to create | ||||
a second instance, the first should be returned. | ||||
""" | ||||
_instances = {} | ||||
def __new__(cls, *p, **k): | ||||
instances = cls._instances | ||||
clskey = str(cls) | ||||
if clskey not in instances: | ||||
instances[clskey] = {} | ||||
instances = instances[clskey] | ||||
key = cls._key(*p, **k) | ||||
if key not in instances: | ||||
instances[key] = super(KeyedInstance, cls).__new__(cls) | ||||
return instances[key] | ||||
@classmethod | ||||
def _key(cls, *p, **k): | ||||
"""Given a unique identifier, return a dictionary key | ||||
This should be overridden by child classes, to specify which parameters | ||||
should determine an object's uniqueness | ||||
""" | ||||
raise NotImplementedError() | ||||
@classmethod | ||||
def clear(cls): | ||||
# Allow cls.clear() as well as uniqueInstance.clear(cls) | ||||
if str(cls) in cls._instances: | ||||
del cls._instances[str(cls)] | ||||