Created
January 29, 2012 11:37
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Object caching metaclass
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# Metaclass for caching objects based on constructor argument | |
class Cached(type): | |
def __new__(cls, name, bases, dct): | |
dct['_cache'] = {} | |
return super(Cached, cls).__new__(cls, name, bases, dct) | |
def __call__(cls, a): | |
try: | |
return cls._cache[a] | |
except KeyError: | |
o = super(Cached, cls).__call__(a) | |
cls._cache[a] = o | |
return o | |
class C(object): | |
__metaclass__ = Cached | |
def __init__(self, i): | |
print "C", i | |
self.i = i | |
class D(object): | |
__metaclass__ = Cached | |
def __init__(self, i): | |
print "D", i | |
self.i = i | |
a = C(1) | |
b = C(2) | |
c = C(1) | |
d = D(1) | |
print a is c | |
print a is d | |
print C._cache | |
print D._cache |
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