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LSST Data Management Base Package
readProxy.py
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1 #!/usr/bin/env python
2 
3 #
4 # LSST Data Management System
5 # Copyright 2008, 2009, 2010 LSST Corporation.
6 #
7 # This product includes software developed by the
8 # LSST Project (http://www.lsst.org/).
9 #
10 # This program is free software: you can redistribute it and/or modify
11 # it under the terms of the GNU General Public License as published by
12 # the Free Software Foundation, either version 3 of the License, or
13 # (at your option) any later version.
14 #
15 # This program is distributed in the hope that it will be useful,
16 # but WITHOUT ANY WARRANTY; without even the implied warranty of
17 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 # GNU General Public License for more details.
19 #
20 # You should have received a copy of the LSST License Statement and
21 # the GNU General Public License along with this program. If not,
22 # see <http://www.lsstcorp.org/LegalNotices/>.
23 #
24 
25 # -*- python -*-
26 
27 """This module defines the ReadProxy class."""
28 
29 from .persistence import ReadProxyBase
30 
31 
32 class ReadProxy(ReadProxyBase):
33  """ReadProxy provides a lazy-loading object that is initialized by a
34  callback function set in ReadProxy's constructor. Adapted from
35  peak.util.proxies.LazyProxy, which was written by Phillip J. Eby
36  (peak@eby-sarna.com)."""
37 
38  __slots__ = ('__cache__', '__callback__')
39 
40  def __init__(self, func):
41  ReadProxyBase.__init__(self)
42  set_callback(self, func)
43 
44  def __getattr__(self, attr):
45  getattr(self.__subject__, attr)
46 
47  def __setattr__(self, attr, val):
48  setattr(self.__subject__, attr, val)
49 
50  def __delattr__(self, attr):
51  delattr(self.__subject__, attr)
52 
53  def __bool__(self):
54  return bool(self.__subject__)
55 
56  def __getitem__(self, arg):
57  return self.__subject__[arg]
58 
59  def __setitem__(self, arg, val):
60  self.__subject__[arg] = val
61 
62  def __delitem__(self, arg):
63  del self.__subject__[arg]
64 
65  def __getslice__(self, i, j):
66  return self.__subject__[i:j]
67 
68  def __setslice__(self, i, j, val):
69  self.__subject__[i:j] = val
70 
71  def __delslice__(self, i, j):
72  del self.__subject__[i:j]
73 
74  def __contains__(self, ob):
75  return ob in self.__subject__
76 
77  for name in 'repr str hash len abs complex int long float iter oct hex'.split():
78  exec("def __%s__(self): return %s(self.__subject__)" % (name, name))
79 
80  for name in 'cmp', 'coerce', 'divmod':
81  exec("def __%s__(self, ob): return %s(self.__subject__, ob)" % (name,
82  name))
83 
84  for name, op in [
85  ('lt', '<'), ('gt', '>'), ('le', '<='), ('ge', '>='),
86  ('eq', '=='), ('ne', '!=')
87  ]:
88  exec("def __%s__(self, ob): return self.__subject__ %s ob" % (name, op))
89 
90  for name, op in [('neg', '-'), ('pos', '+'), ('invert', '~')]:
91  exec("def __%s__(self): return %s self.__subject__" % (name, op))
92 
93  for name, op in [
94  ('or', '|'), ('and', '&'), ('xor', '^'),
95  ('lshift', '<<'), ('rshift', '>>'),
96  ('add', '+'), ('sub', '-'), ('mul', '*'), ('div', '/'),
97  ('mod', '%'), ('truediv', '/'), ('floordiv', '//')
98  ]:
99  exec((
100  "def __%(name)s__(self,ob):\n"
101  " return self.__subject__ %(op)s ob\n"
102  "\n"
103  "def __r%(name)s__(self,ob):\n"
104  " return ob %(op)s self.__subject__\n"
105  "\n"
106  "def __i%(name)s__(self,ob):\n"
107  " self.__subject__ %(op)s=ob\n"
108  " return self\n"
109  ) % locals())
110 
111  del name, op
112 
113  # Oddball signatures
114 
115  def __rdivmod__(self, ob):
116  return divmod(ob, self.__subject__)
117 
118  def __pow__(self, *args):
119  return pow(self.__subject__, *args)
120 
121  def __ipow__(self, ob):
122  self.__subject__ **= ob
123  return self
124 
125  def __rpow__(self, ob):
126  return pow(ob, self.__subject__)
127 
128 
129 get_callback = ReadProxy.__callback__.__get__
130 set_callback = ReadProxy.__callback__.__set__
131 get_cache = ReadProxy.__cache__.__get__
132 set_cache = ReadProxy.__cache__.__set__
133 
134 
135 def _subject(self, get_cache=get_cache, set_cache=set_cache):
136  try:
137  return get_cache(self)
138  except AttributeError:
139  set_cache(self, get_callback(self)())
140  return get_cache(self)
141 
142 
143 ReadProxy.__subject__ = property(_subject, set_cache)
144 del _subject