git.fiddlerwoaroof.com
lazy_attributes.py
a3fd722b
 # Copyright (c) 2011 Edward Langley
 # All rights reserved.
 # 
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions
 # are met:
 # 
 # Redistributions of source code must retain the above copyright notice,
 # this list of conditions and the following disclaimer.
 # 
 # Redistributions in binary form must reproduce the above copyright
 # notice, this list of conditions and the following disclaimer in the
 # documentation and/or other materials provided with the distribution.
 # 
 # Neither the name of the project's author nor the names of its
 # contributors may be used to endorse or promote products derived from
 # this software without specific prior written permission.
 # 
 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 # FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 # HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
 # TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 # PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 # LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 # NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 # SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
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 class LazyLoad(object):
     def __init__(self, __func_, *args, **kwargs):
         self.__func = __func_
         self.__args = list(args)
         self.__kwargs = kwargs
     def __get__(self, inst, cls):
         tb = cls.__dict__
         nm = [x for x in tb.keys() if id(tb[x]) == id(self)][0]
         setattr(inst, nm, self.__func(*self.__args, **self.__kwargs))
         return getattr(inst, nm)
 
 def func(a,b,c):
     print a,b,c
     return a+b,c
 
 class a(object):
     b = LazyLoad(func, 1,2,3)
     c = LazyLoad(func, 2,3,4)
     d = LazyLoad(func, 3,4,5)
     __e = LazyLoad(func, 4,5,6)
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     def __str__(self): return str(self.__e)