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__doc__='''Batch class, for iterating over a sequence in batches

$Id: Batch.py,v 1.2 2001/04/27 20:51:20 evan Exp $'''
__version__='$Revision: 1.2 $'[11:-2]

from ExtensionClass import Base

class LazyPrevBatch(Base):
    def __of__(self, parent):
        return Batch(parent._sequence, parent._size,
                     -1, parent.first + parent.overlap,
                     parent.orphan, parent.overlap)

class LazyNextBatch(Base):
    def __of__(self, parent):
        try: parent._sequence[parent.end]
        except IndexError: return None
        return Batch(parent._sequence, parent._size,
                     parent.end - parent.overlap, 0,
                     parent.orphan, parent.overlap)

class Batch(Base):
    """Create a sequence batch"""
    __allow_access_to_unprotected_subobjects__ = 1

    previous = LazyPrevBatch()
    next = LazyNextBatch()
    
    def __init__(self, sequence, size, start=0, end=0,
                 orphan=3, overlap=0):

        start = start + 1

        start,end,sz = opt(start,end,size,orphan,sequence)

        self._sequence = sequence
        self.size = sz
        self._size = size
        self.start = start
        self.end = end
        self.orphan = orphan
        self.overlap = overlap
        self.first = max(start - 1, 0)
        self.length = self.end - self.first
        if self.first == 0:
            self.previous = None
        
        
    def __getitem__(self, index):
        if index < 0:
            if index + self.end < self.first: raise IndexError, index
            return self._sequence[index + self.end]
        
        if index >= self.size: raise IndexError, index
        return self._sequence[index+self.first]

    def __len__(self):
        return self.length

def opt(start,end,size,orphan,sequence):
    if size < 1:
        if start > 0 and end > 0 and end >= start:
            size=end+1-start
        else: size=7

    if start > 0:

        try: sequence[start-1]
        except: start=len(sequence)

        if end > 0:
            if end < start: end=start
        else:
            end=start+size-1
            try: sequence[end+orphan-1]
            except: end=len(sequence)
    elif end > 0:
        try: sequence[end-1]
        except: end=len(sequence)
        start=end+1-size
        if start - 1 < orphan: start=1
    else:
        start=1
        end=start+size-1
        try: sequence[end+orphan-1]
        except: end=len(sequence)
    return start,end,size
