SF patch #872326: Generator expression implementation

(Code contributed by Jiwon Seo.)

The documentation portion of the patch is being re-worked and will be
checked-in soon.  Likewise, PEP 289 will be updated to reflect Guido's
rationale for the design decisions on binding behavior (as described in
in his patch comments and in discussions on python-dev).

The test file, test_genexps.py, is written in doctest format and is
meant to exercise all aspects of the the patch.  Further additions are
welcome from everyone.  Please stress test this new feature as much as
possible before the alpha release.

Lib/compiler/ast.py

@@ -1236,6 +1236,82 @@ class ListCompFor(Node):
     def __repr__(self):
         return "ListCompFor(%s, %s, %s)" % (repr(self.assign), repr(self.list), repr(self.ifs))
 
+class GenExpr(Node):
+    nodes["genexpr"] = "GenExpr"
+    def __init__(self, code):
+        self.code = code
+        self.argnames = ['[outmost-iterable]']
+        self.varargs = self.kwargs = None
+
+    def getChildren(self):
+        return self.code,
+
+    def getChildNodes(self):
+        return self.code,
+
+    def __repr__(self):
+        return "GenExpr(%s)" % (repr(self.code),)
+
+class GenExprInner(Node):
+    nodes["genexprinner"] = "GenExprInner"
+    def __init__(self, expr, quals):
+        self.expr = expr
+        self.quals = quals
+
+    def getChildren(self):
+        children = []
+        children.append(self.expr)
+        children.extend(flatten(self.quals))
+        return tuple(children)
+
+    def getChildNodes(self):
+        nodelist = []
+        nodelist.append(self.expr)
+        nodelist.extend(flatten_nodes(self.quals))
+        return tuple(nodelist)
+
+    def __repr__(self):
+        return "GenExprInner(%s, %s)" % (repr(self.expr), repr(self.quals))
+
+class GenExprFor(Node):
+    nodes["genexprfor"] = "GenExprFor"
+    def __init__(self, assign, iter, ifs):
+        self.assign = assign
+        self.iter = iter
+        self.ifs = ifs
+        self.is_outmost = False
+
+    def getChildren(self):
+        children = []
+        children.append(self.assign)
+        children.append(self.iter)
+        children.extend(flatten(self.ifs))
+        return tuple(children)
+
+    def getChildNodes(self):
+        nodelist = []
+        nodelist.append(self.assign)
+        nodelist.append(self.iter)
+        nodelist.extend(flatten_nodes(self.ifs))
+        return tuple(nodelist)
+
+    def __repr__(self):
+        return "GenExprFor(%s, %s, %s)" % (repr(self.assign), repr(self.iter), repr(self.ifs))
+
+class GenExprIf(Node):
+    nodes["genexprif"] = "GenExprIf"
+    def __init__(self, test):
+        self.test = test
+
+    def getChildren(self):
+        return self.test,
+
+    def getChildNodes(self):
+        return self.test,
+
+    def __repr__(self):
+        return "GenExprIf(%s)" % (repr(self.test),)
+
 klasses = globals()
 for k in nodes.keys():
     nodes[k] = klasses[nodes[k]]