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cachingSkyMap.py
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1 from builtins import range
2 #
3 # LSST Data Management System
4 # Copyright 2008-2012 LSST Corporation.
5 #
6 # This product includes software developed by the
7 # LSST Project (http://www.lsst.org/).
8 #
9 # This program is free software: you can redistribute it and/or modify
10 # it under the terms of the GNU General Public License as published by
11 # the Free Software Foundation, either version 3 of the License, or
12 # (at your option) any later version.
13 #
14 # This program is distributed in the hope that it will be useful,
15 # but WITHOUT ANY WARRANTY; without even the implied warranty of
16 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 # GNU General Public License for more details.
18 #
19 # You should have received a copy of the LSST License Statement and
20 # the GNU General Public License along with this program. If not,
21 # see <http://www.lsstcorp.org/LegalNotices/>.
22 #
23 
24 from .baseSkyMap import BaseSkyMap
25 
26 
27 class CachingSkyMap(BaseSkyMap):
28  """A SkyMap that generates its tracts on request and caches them
29 
30  A subclass should define
31  * __init__ to calculate the required number of tracts (and pass it up)
32  * generateTract to generate a tract
33 
34  Subclassers should also check that the arguments to the constructor are
35  consistent with the below __reduce__ method.
36  """
37 
38  def __init__(self, numTracts, config=None, version=0):
39  super(CachingSkyMap, self).__init__(config)
40  self._numTracts = numTracts
41  self._tractCache = [None] * self._numTracts
42  self._tractInfo = None # We shouldn't need this; we will generate tracts on demand
43  self._version = version
44 
45  def __reduce__(self):
46  """To support pickling
47 
48  Warning: This method assumes that the constructor should be defined:
49  __init__(self, config, version=defaultVersion)
50  The use of 'config' is effectively set by the registry mechanism.
51  If additional optional arguments are added, this method should be
52  overridden to correspond.
53  """
54  return (self.__class__, (self.config, self._version))
55 
56  def __iter__(self):
57  """Iterator over tracts"""
58  for i in range(self._numTracts):
59  yield self[i]
60 
61  def __len__(self):
62  """Length is number of tracts"""
63  return self._numTracts
64 
65  def __getitem__(self, index):
66  """Get the TractInfo for a particular index
67 
68  The tract is returned from a cache, if available, otherwise generated
69  on the fly.
70  """
71  if index < 0 or index > self._numTracts:
72  raise IndexError("Index out of range: %d vs %d" % (index, self._numTracts))
73  if self._tractCache[index] is not None:
74  return self._tractCache[index]
75  tract = self.generateTract(index)
76  self._tractCache[index] = tract
77  return tract
78 
79  def generateTract(self, index):
80  """Generate the TractInfo for the particular index"""
81  raise NotImplementedError("Subclasses must define this method.")