better iterbetter (tx Emyr Thomas for the idea)

Author: anandology

web/utils.py

@@ -523,13 +523,31 @@ class IterBetter:
  Traceback (most recent call last):
  ...
  IndexError: already passed 3
+
+ For boolean test, IterBetter peeps at first value in the itertor without effecting the iteration.
+
+ >>> c = iterbetter(iter(range(5)))
+ >>> bool(c)
+ True
+ >>> list(c)
+ [0, 1, 2, 3, 4]
+ >>> c = iterbetter(iter([]))
+ >>> bool(c)
+ False
+ >>> list(c)
+ []
  """
  def __init__(self, iterator): 
  self.i, self.c = iterator, 0
+
  def __iter__(self): 
+ if hasattr(self, "_head"):
+ yield self._head
+
  while 1: 
  yield self.i.next()
  self.c += 1
+
  def __getitem__(self, i):
  #todo: slices
  if i < self.c: 
@@ -545,7 +563,18 @@ def __getitem__(self, i):
  raise IndexError, str(i)
 
  def __nonzero__(self):
- return len(self) != 0
+ if hasattr(self, "__len__"):
+ return len(self) != 0
+ elif hasattr(self, "_head"):
+ return True
+ else:
+ try:
+ self._head = self.i.next()
+ except StopIteration:
+ return False
+ else:
+ return True
+ 
 
 iterbetter = IterBetter