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#!/usr/bin/env python
# -*- coding: utf-8 -*-
class cachedproperty(object):
'''
>>> class C(object):
... def __init__(self, x):
... self._x = x
... def get_x(self):
... print "getting x"
... return self._x
...
... def set_x(self, newx):
... print "setting x with %s" % newx
... self._x = newx
... def del_x(self):
... self._x = "i am deleted"
...
... x = cachedproperty(get_x, set_x, del_x)
... other_x = cachedproperty(get_x, set_x)
>>> c = C(5)
>>> c.x
getting x
5
# cached.
>>> c.x
5
>>> c.x, c.y = 6, 7
setting x with 6
# uncached.
>>> c.x
getting x
6
>>> c.x, c.y
(6, 7)
>>> c.y = 35
>>> c.x, c.y
(6, 35)
# ok with multiple instances.
>>> d = C(4)
>>> d.x
getting x
4
>>> c.x
6
>>> c.other_x = 7
setting x with 7
>>> c.get_x()
getting x
7
>>> del c.x
>>> c.x
getting x
\'i am deleted\'
>>> c.set_x(22)
setting x with 22
# but the property cant know about it...
>>> c.x
\'i am deleted\'
'''
__slots__ = ("fget", "fset", "fdel", "n")
def __init__(self, fget=None, fset=None, fdel=None):
self.fget = fget
self.fset = fset
self.fdel = fdel
self.n = "__" + fget.__name__
def __get__(self, o, otype=None):
if o is None:
return None
if self.n in o.__dict__:
return (o.__dict__)[self.n]
result = (o.__dict__)[self.n] = self.fget(o)
return result
def __set__(self, o, value):
if self.fset is None:
raise AttributeError("unsettable %s (with %s)" % (self.n, value))
else:
if self.n in o.__dict__:
del (o.__dict__)[self.n]
self.fset(o, value)
def __delete__(self, o):
if self.fdel is None:
raise AttributeError("undeletable %s (with %s)" % (self.n, value))
else:
if self.n in o.__dict__:
del (o.__dict__)[self.n]
self.fdel(o)
if __name__ == "__main__":
import doctest
doctest.testmod()
|
