django/utils/itercompat.py

   1 """
   2 Providing iterator functions that are not in all version of Python we support.
   3 Where possible, we try to use the system-native version and only fall back to
   4 these implementations if necessary.
   5 """
   6
   7 import itertools
   8
   9 def compat_tee(iterable):
  10     """
  11     Return two independent iterators from a single iterable.
  12
  13     Based on http://www.python.org/doc/2.3.5/lib/itertools-example.html
  14     """
  15     # Note: Using a dictionary and a list as the default arguments here is
  16     # deliberate and safe in this instance.
  17     def gen(next, data={}, cnt=[0]):
  18         dpop = data.pop
  19         for i in itertools.count():
  20             if i == cnt[0]:
  21                 item = data[i] = next()
  22                 cnt[0] += 1
  23             else:
  24                 item = dpop(i)
  25             yield item
  26     next = iter(iterable).next
  27     return gen(next), gen(next)
  28
  29 def groupby(iterable, keyfunc=None):
  30     """
  31     Taken from http://docs.python.org/lib/itertools-functions.html
  32     """
  33     if keyfunc is None:
  34         keyfunc = lambda x:x
  35     iterable = iter(iterable)
  36     l = [iterable.next()]
  37     lastkey = keyfunc(l[0])
  38     for item in iterable:
  39         key = keyfunc(item)
  40         if key != lastkey:
  41             yield lastkey, l
  42             lastkey = key
  43             l = [item]
  44         else:
  45             l.append(item)
  46     yield lastkey, l
  47
  48 # Not really in itertools, since it's a builtin in Python 2.4 and later, but it
  49 # does operate as an iterator.
  50 def reversed(data):
  51     for index in xrange(len(data)-1, -1, -1):
  52         yield data[index]
  53
  54 if hasattr(itertools, 'tee'):
  55     tee = itertools.tee
  56 else:
  57     tee = compat_tee
  58 if hasattr(itertools, 'groupby'):
  59     groupby = itertools.groupby
  60
  61 def is_iterable(x):
  62     "A implementation independent way of checking for iterables"
  63     try:
  64         iter(x)
  65     except TypeError:
  66         return False
  67     else:
  68         return True
  69