C Code:

* Removed the ifilter flag wart by splitting it into two simpler functions.
* Fixed comment tabbing in C code.
* Factored module start-up code into a loop.

Documentation:
* Re-wrote introduction.
* Addede examples for quantifiers.
* Simplified python equivalent for islice().
* Documented split of ifilter().

Sets.py:
* Replace old ifilter() usage with new.

Doc/lib/libitertools.tex

@@ -12,45 +12,43 @@ This module implements a number of iterator building blocks inspired
 by constructs from the Haskell and SML programming languages.  Each
 has been recast in a form suitable for Python.
 
-With the advent of iterators and generators in Python 2.3, each of
-these tools can be expressed easily and succinctly in pure python.
-Rather duplicating what can already be done, this module emphasizes
-providing value in other ways:
-
-\begin{itemize}
-
-    \item Instead of constructing an over-specialized toolset, this module
-        provides basic building blocks that can be readily combined.
-
-        For instance, SML provides a tabulation tool: \code{tabulate(\var{f})}
-        which produces a sequence \code{f(0), f(1), ...}.  This toolbox
-        takes a different approach of providing \function{imap()} and
-        \function{count()} which can be combined to form
-        \code{imap(\var{f}, count())} and produce an equivalent result.
-
-    \item Some tools were dropped because they offer no advantage over their
-        pure python counterparts or because their behavior was too
-        surprising.
-
-        For instance, SML provides a tool:  \code{cycle(\var{seq})} which
-        loops over the sequence elements and then starts again when the
-        sequence is exhausted.  The surprising behavior is the need for
-        significant auxiliary storage (unusual for iterators).  Also, it
-        is trivially implemented in python with almost no performance
-        penalty.
-
-    \item Another source of value comes from standardizing a core set of tools
-        to avoid the readability and reliability problems that arise when many
-        different individuals create their own slightly varying implementations
-        each with their own quirks and naming conventions.
-
-    \item Whether cast in pure python form or C code, tools that use iterators
-        are more memory efficient (and faster) than their list based counterparts.
-        Adopting the principles of just-in-time manufacturing, they create
-        data when and where needed instead of consuming memory with the
-        computer equivalent of ``inventory''.
-
-\end{itemize}
+The module standardizes a core set of fast, memory efficient tools
+that are useful by themselves or in combination.  Standardization helps
+avoid the readability and reliability problems which arise when many
+different individuals create their own slightly varying implementations,
+each with their own quirks and naming conventions.
+
+The tools are designed to combine readily with each another.  This makes
+it easy to construct more specialized tools succinctly and efficiently
+in pure Python.
+
+For instance, SML provides a tabulation tool: \code{tabulate(\var{f})}
+which produces a sequence \code{f(0), f(1), ...}.  This toolbox
+provides \function{imap()} and \function{count()} which can be combined
+to form \code{imap(\var{f}, count())} and produce an equivalent result.
+
+Whether cast in pure python form or C code, tools that use iterators
+are more memory efficient (and faster) than their list based counterparts.
+Adopting the principles of just-in-time manufacturing, they create
+data when and where needed instead of consuming memory with the
+computer equivalent of ``inventory''.
+
+Some tools were omitted from the module because they offered no
+advantage over their pure python counterparts or because their behavior
+was too surprising.
+
+For instance, SML provides a tool:  \code{cycle(\var{seq})} which
+loops over the sequence elements and then starts again when the
+sequence is exhausted.  The surprising behavior is the need for
+significant auxiliary storage (which is unusual for an iterator).
+If needed, the tool is readily constructible using pure Python.
+
+Other tools are being considered for inclusion in future versions of the
+module.  For instance, the function
+\function{chain(\var{it0}, \var{it1}, ...})} would return elements from
+the first iterator until it was exhausted and then move on to each
+successive iterator.  The module author welcomes suggestions for other
+basic building blocks.
 
 \begin{seealso}
   \seetext{The Standard ML Basis Library,
@@ -107,24 +105,36 @@ by functions or loops that truncate the stream.
   \end{verbatim}
 \end{funcdesc}
 
-\begin{funcdesc}{ifilter}{predicate, iterable \optional{, invert}}
+\begin{funcdesc}{ifilter}{predicate, iterable}
   Make an iterator that filters elements from iterable returning only
-  those for which the predicate is \code{True}.  If
-  \var{invert} is \code{True}, then reverse the process and pass through
-  only those elements for which the predicate is \code{False}.
-  If \var{predicate} is \code{None}, return the items that are true
-  (or false if \var{invert} has been set).  Equivalent to:
+  those for which the predicate is \code{True}.
+  If \var{predicate} is \code{None}, return the items that are true.
+  Equivalent to:
 
   \begin{verbatim}
-     def ifilter(predicate, iterable, invert=False):
-         iterable = iter(iterable)
-         while True:
-             x = iterable.next()
-             if predicate is None:
-                  b = bool(x)
-             else:
-                  b = bool(predicate(x))
-             if not invert and b or invert and not b:
+     def ifilter(predicate, iterable):
+         if predicate is None:
+             def predicate(x):
+                 return x
+         for x in iterable:
+             if predicate(x):
+                 yield x
+  \end{verbatim}
+\end{funcdesc}
+
+\begin{funcdesc}{ifilterfalse}{predicate, iterable}
+  Make an iterator that filters elements from iterable returning only
+  those for which the predicate is \code{False}.
+  If \var{predicate} is \code{None}, return the items that are false.
+  Equivalent to:
+
+  \begin{verbatim}
+     def ifilterfalse(predicate, iterable):
+         if predicate is None:
+             def predicate(x):
+                 return x
+         for x in iterable:
+             if not predicate(x):
                  yield x
   \end{verbatim}
 \end{funcdesc}
@@ -169,21 +179,17 @@ by functions or loops that truncate the stream.
 
   \begin{verbatim}
      def islice(iterable, *args):
-         iterable = iter(iterable)
          s = slice(*args)
          next = s.start or 0
          stop = s.stop
          step = s.step or 1
-         cnt = 0
-         while True:
-              while cnt < next:
-                   dummy = iterable.next()
-                   cnt += 1
-              if cnt >= stop:
-                   break
-              yield iterable.next()
-              cnt += 1
-              next += step
+         for cnt, element in enumerate(iterable):
+             if cnt < next:
+                 continue
+             if cnt >= stop:
+                 break
+             yield element
+             next += step
   \end{verbatim}
 \end{funcdesc}
 
@@ -324,6 +330,18 @@ from building blocks.
 
 >>> def nth(iterable, n):
 ...     "Returns the nth item"
-...     return islice(iterable, n, n+1).next()
+...     return list(islice(iterable, n, n+1))
+
+>>> def all(pred, seq):
+...     "Returns True if pred(x) is True for every element in the iterable"
+...     return not nth(ifilterfalse(pred, seq), 0)
+
+>>> def some(pred, seq):
+...     "Returns True if pred(x) is True at least one element in the iterable"
+...     return bool(nth(ifilter(pred, seq), 0))
+
+>>> def no(pred, seq):
+...     "Returns True if pred(x) is False for every element in the iterable"
+...     return not nth(ifilter(pred, seq), 0)
 
 \end{verbatim}

Lib/sets.py

@@ -57,7 +57,7 @@ what's tested is actually `z in y'.
 
 
 __all__ = ['BaseSet', 'Set', 'ImmutableSet']
-from itertools import ifilter
+from itertools import ifilter, ifilterfalse
 
 class BaseSet(object):
     """Common base class for mutable and immutable sets."""
@@ -204,9 +204,9 @@ class BaseSet(object):
         value = True
         selfdata = self._data
         otherdata = other._data
-        for elt in ifilter(otherdata.has_key, selfdata, True):
+        for elt in ifilterfalse(otherdata.has_key, selfdata):
             data[elt] = value
-        for elt in ifilter(selfdata.has_key, otherdata, True):
+        for elt in ifilterfalse(selfdata.has_key, otherdata):
             data[elt] = value
         return result
 
@@ -227,7 +227,7 @@ class BaseSet(object):
         result = self.__class__()
         data = result._data
         value = True
-        for elt in ifilter(other._data.has_key, self, True):
+        for elt in ifilterfalse(other._data.has_key, self):
             data[elt] = value
         return result
 
@@ -260,7 +260,7 @@ class BaseSet(object):
         self._binary_sanity_check(other)
         if len(self) > len(other):  # Fast check for obvious cases
             return False
-        for elt in ifilter(other._data.has_key, self, True):
+        for elt in ifilterfalse(other._data.has_key, self):
             return False
         return True
 
@@ -269,7 +269,7 @@ class BaseSet(object):
         self._binary_sanity_check(other)
         if len(self) < len(other):  # Fast check for obvious cases
             return False
-        for elt in ifilter(self._data.has_key, other, True):
+        for elt in ifilterfalse(self._data.has_key, other):
             return False
         return True
 

Lib/test/test_itertools.py

@@ -13,12 +13,19 @@ class TestBasicOps(unittest.TestCase):
         def isEven(x):
             return x%2==0
         self.assertEqual(list(ifilter(isEven, range(6))), [0,2,4])
-        self.assertEqual(list(ifilter(isEven, range(6), True)), [1,3,5])
         self.assertEqual(list(ifilter(None, [0,1,0,2,0])), [1,2])
         self.assertRaises(TypeError, ifilter)
         self.assertRaises(TypeError, ifilter, 3)
         self.assertRaises(TypeError, ifilter, isEven, 3)
-        self.assertRaises(TypeError, ifilter, isEven, [3], True, 4)
+
+    def test_ifilterfalse(self):
+        def isEven(x):
+            return x%2==0
+        self.assertEqual(list(ifilterfalse(isEven, range(6))), [1,3,5])
+        self.assertEqual(list(ifilterfalse(None, [0,1,0,2,0])), [0,0,0])
+        self.assertRaises(TypeError, ifilterfalse)
+        self.assertRaises(TypeError, ifilterfalse, 3)
+        self.assertRaises(TypeError, ifilterfalse, isEven, 3)
 
     def test_izip(self):
         ans = [(x,y) for x, y in izip('abc',count())]
@@ -133,7 +140,19 @@ Samuele
 
 >>> def nth(iterable, n):
 ...     "Returns the nth item"
-...     return islice(iterable, n, n+1).next()
+...     return list(islice(iterable, n, n+1))
+
+>>> def all(pred, seq):
+...     "Returns True if pred(x) is True for every element in the iterable"
+...     return not nth(ifilterfalse(pred, seq), 0)
+
+>>> def some(pred, seq):
+...     "Returns True if pred(x) is True at least one element in the iterable"
+...     return bool(nth(ifilter(pred, seq), 0))
+
+>>> def no(pred, seq):
+...     "Returns True if pred(x) is False for every element in the iterable"
+...     return not nth(ifilter(pred, seq), 0)
 
 """