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Location: kallithea/rhodecode/lib/dbmigrate/migrate/versioning/util/keyedinstance.py - annotation
260a7a01b054
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follow Python conventions for boolean values
True and False might be singletons and the "default" values for "boolean"
expressions, but "all" values in Python has a boolean value and should be
evaluated as such. Checking with 'is True' and 'is False' is thus confusing,
error prone and unnessarily complex.
If we anywhere rely and nullable boolean fields from the database layer and
don't want the null value to be treated as False then we should check
explicitly for null with 'is None'.
True and False might be singletons and the "default" values for "boolean"
expressions, but "all" values in Python has a boolean value and should be
evaluated as such. Checking with 'is True' and 'is False' is thus confusing,
error prone and unnessarily complex.
If we anywhere rely and nullable boolean fields from the database layer and
don't want the null value to be treated as False then we should check
explicitly for null with 'is None'.
9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 6832ef664673 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 6832ef664673 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 9753e0907827 | #!/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 = dict()
def __new__(cls, *p, **k):
instances = cls._instances
clskey = str(cls)
if clskey not in instances:
instances[clskey] = dict()
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)]
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