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1. Group items from iterable into chunks of specified size.

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   Only tested with Python 2.5, but should work with 2.3+

    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]) ]
   

   Posted by rmurri to python itertools ... saved by 1 person ... 0 comments ... 10 months, 2 weeks

2. Alter items in a sequence according to a translation table

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   This is the analogue of Python `str.translate` or `unicode.translate` for general iterables (lists, tuples, etc.) Tested with Python 2.5

    1 class itranslate:
    2     """Return items from a sequence, substituting them as specified.
    3 
    4     First c'tor argument `subst` is a dictionary, specifying
    5     substitutions to be applied.  If an item matches a key of the
    6     `subst` dictionary, the associated dictionary value is returned
    7     instead; unless the value is `None`, in which case the item is
    8     skipped altogether.
    9 
   10     *Note:* you should use an appropriate `dict`-subclass if you want
   11      to translate items which are not immutable.
   12     
   13     Examples::
   14       >>> list(itranslate({0:None, 3:2}, [2,1,0,0,1,3]))
   15       [2, 1, 1, 2]
   16     """
   17     def __init__(self, subst, iterable):
   18         self.mappings = subst
   19         self.iterable = iter(iterable)
   20     def __iter__(self):
   21         return self
   22     def next(self):
   23         while True:
   24             next = self.iterable.next()
   25             if not self.mappings.has_key(next):
   26                 return next
   27             translated = self.mappings[next]
   28             if translated is None:
   29                 # skip this item
   30                 continue
   31             return translated
   

   Posted by rmurri to python itertools ... saved by 2 persons ... 0 comments ... 10 months, 4 weeks

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