Friendsnippets

 1 class chunks(object):
 2     """Lump items from iterable into chunks of specified size.
 3 
 4     Instanciate the iterator passing a sequence of chunk sizes in
 5     argument 1 and an iterable to consume in argument 2::
 6 
 7       >>> for c in chunks([1,1,1], xrange(3)): print c
 8       [0]
 9       [1]
10       [2]
11 
12     The list of chunk sizes may be any kind of sequence, for instance
13     a tuple or even a (possibly infinite) iterable::
14     
15       >>> list(chunks((1,2,3), range(6)))
16       [[0], [1, 2], [3, 4, 5]]
17 
18     The total size of the chunks may be less than the size of the
19     iterator: remaining items in the iterator are not consumed::
20 
21       >>> for c in chunks([1,2], range(6)): print c
22       [0]
23       [1, 2]
24 
25     As a special case, if a chunk has size 0, then an empty list is
26     returned in its place and no item from iterable is consumed::
27     
28       >>> for c in chunks([2,0,2], range(4)): print c
29       [0, 1]
30       []
31       [2, 3]
32       
33     """
34     def __init__(self, sizes, iterable):
35         """Constructor, taking sequence of chunk sizes and iterable to
36         consume."""
37         self.current_chunk = -1
38         self.sizes = sizes
39         self.iterable = iter(iterable)
40     def __iter__(self):
41         return self
42     def next(self):
43         """Return next chunk."""
44         self.current_chunk += 1
45         if self.current_chunk >= len(self.sizes):
46             raise StopIteration
47         return [ self.iterable.next()
48                    for x in xrange(self.sizes[self.current_chunk]) ]