roundup/cgi/ZTUtils/Batch.py

   1 ##############################################################################
   2 #
   3 # Copyright (c) 2001 Zope Corporation and Contributors. All Rights Reserved.
   4 #
   5 # This software is subject to the provisions of the Zope Public License,
   6 # Version 2.0 (ZPL).  A copy of the ZPL should accompany this distribution.
   7 # THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
   8 # WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
   9 # WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
  10 # FOR A PARTICULAR PURPOSE
  11 #
  12 ##############################################################################
  13 __doc__='''Batch class, for iterating over a sequence in batches
  14
  15 $Id: Batch.py,v 1.2 2002-09-11 23:54:26 richard Exp $'''
  16 __version__='$Revision: 1.2 $'[11:-2]
  17
  18 class LazyPrevBatch:
  19     def __of__(self, parent):
  20         return Batch(parent._sequence, parent._size,
  21                      parent.first - parent._size + parent.overlap, 0,
  22                      parent.orphan, parent.overlap)
  23
  24 class LazyNextBatch:
  25     def __of__(self, parent):
  26         try: parent._sequence[parent.end]
  27         except IndexError: return None
  28         return Batch(parent._sequence, parent._size,
  29                      parent.end - parent.overlap, 0,
  30                      parent.orphan, parent.overlap)
  31
  32 class LazySequenceLength:
  33     def __of__(self, parent):
  34         parent.sequence_length = l = len(parent._sequence)
  35         return l
  36
  37 class Batch:
  38     """Create a sequence batch"""
  39     __allow_access_to_unprotected_subobjects__ = 1
  40
  41     previous = LazyPrevBatch()
  42     next = LazyNextBatch()
  43     sequence_length = LazySequenceLength()
  44
  45     def __init__(self, sequence, size, start=0, end=0,
  46                  orphan=0, overlap=0):
  47         '''Encapsulate "sequence" in batches of "size".
  48
  49         Arguments: "start" and "end" are 0-based indexes into the
  50         sequence.  If the next batch would contain no more than
  51         "orphan" elements, it is combined with the current batch.
  52         "overlap" is the number of elements shared by adjacent
  53         batches.  If "size" is not specified, it is computed from
  54         "start" and "end".  Failing that, it is 7.
  55
  56         Attributes: Note that the "start" attribute, unlike the
  57         argument, is a 1-based index (I know, lame).  "first" is the
  58         0-based index.  "length" is the actual number of elements in
  59         the batch.
  60
  61         "sequence_length" is the length of the original, unbatched, sequence
  62         '''
  63
  64         start = start + 1
  65
  66         start,end,sz = opt(start,end,size,orphan,sequence)
  67
  68         self._sequence = sequence
  69         self.size = sz
  70         self._size = size
  71         self.start = start
  72         self.end = end
  73         self.orphan = orphan
  74         self.overlap = overlap
  75         self.first = max(start - 1, 0)
  76         self.length = self.end - self.first
  77         if self.first == 0:
  78             self.previous = None
  79
  80
  81     def __getitem__(self, index):
  82         if index < 0:
  83             if index + self.end < self.first: raise IndexError, index
  84             return self._sequence[index + self.end]
  85
  86         if index >= self.length: raise IndexError, index
  87         return self._sequence[index + self.first]
  88
  89     def __len__(self):
  90         return self.length
  91
  92 def opt(start,end,size,orphan,sequence):
  93     if size < 1:
  94         if start > 0 and end > 0 and end >= start:
  95             size=end+1-start
  96         else: size=7
  97
  98     if start > 0:
  99
 100         try: sequence[start-1]
 101         except IndexError: start=len(sequence)
 102
 103         if end > 0:
 104             if end < start: end=start
 105         else:
 106             end=start+size-1
 107             try: sequence[end+orphan-1]
 108             except IndexError: end=len(sequence)
 109     elif end > 0:
 110         try: sequence[end-1]
 111         except IndexError: end=len(sequence)
 112         start=end+1-size
 113         if start - 1 < orphan: start=1
 114     else:
 115         start=1
 116         end=start+size-1
 117         try: sequence[end+orphan-1]
 118         except IndexError: end=len(sequence)
 119     return start,end,size