#
#  Copyright (c) 2007 Helmut Merz helmutm@cy55.de
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software
#  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#

"""
Advanced properties, esp the lazy one...

Based on zope.cachedescriptors.property.Lazy

$Id$
"""

class lzprop(object):
    """Declare lazy properties that are calculated only if needed,
       and just once.

       See property.txt for example usage.
    """

    def __init__(self, func):
        self.func = func

    def __get__(self, inst, class_):
        if inst is None: return self
        value = self.func(inst)
        inst.__dict__[self.func.__name__] = value
        return value