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 1.3 2004-02-11 23:55:09 richard Exp $'''
  16 __docformat__ = 'restructuredtext'
  17 __version__='$Revision: 1.3 $'[11:-2]
  18
  19 class LazyPrevBatch:
  20     def __of__(self, parent):
  21         return Batch(parent._sequence, parent._size,
  22                      parent.first - parent._size + parent.overlap, 0,
  23                      parent.orphan, parent.overlap)
  24
  25 class LazyNextBatch:
  26     def __of__(self, parent):
  27         try: parent._sequence[parent.end]
  28         except IndexError: return None
  29         return Batch(parent._sequence, parent._size,
  30                      parent.end - parent.overlap, 0,
  31                      parent.orphan, parent.overlap)
  32
  33 class LazySequenceLength:
  34     def __of__(self, parent):
  35         parent.sequence_length = l = len(parent._sequence)
  36         return l
  37
  38 class Batch:
  39     """Create a sequence batch"""
  40     __allow_access_to_unprotected_subobjects__ = 1
  41
  42     previous = LazyPrevBatch()
  43     next = LazyNextBatch()
  44     sequence_length = LazySequenceLength()
  45
  46     def __init__(self, sequence, size, start=0, end=0,
  47                  orphan=0, overlap=0):
  48         '''Encapsulate "sequence" in batches of "size".
  49
  50         Arguments: "start" and "end" are 0-based indexes into the
  51         sequence.  If the next batch would contain no more than
  52         "orphan" elements, it is combined with the current batch.
  53         "overlap" is the number of elements shared by adjacent
  54         batches.  If "size" is not specified, it is computed from
  55         "start" and "end".  Failing that, it is 7.
  56
  57         Attributes: Note that the "start" attribute, unlike the
  58         argument, is a 1-based index (I know, lame).  "first" is the
  59         0-based index.  "length" is the actual number of elements in
  60         the batch.
  61
  62         "sequence_length" is the length of the original, unbatched, sequence
  63         '''
  64
  65         start = start + 1
  66
  67         start,end,sz = opt(start,end,size,orphan,sequence)
  68
  69         self._sequence = sequence
  70         self.size = sz
  71         self._size = size
  72         self.start = start
  73         self.end = end
  74         self.orphan = orphan
  75         self.overlap = overlap
  76         self.first = max(start - 1, 0)
  77         self.length = self.end - self.first
  78         if self.first == 0:
  79             self.previous = None
  80
  81
  82     def __getitem__(self, index):
  83         if index < 0:
  84             if index + self.end < self.first: raise IndexError, index
  85             return self._sequence[index + self.end]
  86
  87         if index >= self.length: raise IndexError, index
  88         return self._sequence[index + self.first]
  89
  90     def __len__(self):
  91         return self.length
  92
  93 def opt(start,end,size,orphan,sequence):
  94     if size < 1:
  95         if start > 0 and end > 0 and end >= start:
  96             size=end+1-start
  97         else: size=7
  98
  99     if start > 0:
 100
 101         try: sequence[start-1]
 102         except IndexError: start=len(sequence)
 103
 104         if end > 0:
 105             if end < start: end=start
 106         else:
 107             end=start+size-1
 108             try: sequence[end+orphan-1]
 109             except IndexError: end=len(sequence)
 110     elif end > 0:
 111         try: sequence[end-1]
 112         except IndexError: end=len(sequence)
 113         start=end+1-size
 114         if start - 1 < orphan: start=1
 115     else:
 116         start=1
 117         end=start+size-1
 118         try: sequence[end+orphan-1]
 119         except IndexError: end=len(sequence)
 120     return start,end,size