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.

9 files changed, 584 insertions, 18 deletions

diff --git a/Lib/compiler/ast.py b/Lib/compiler/ast.py
index a10225b..064df50 100644
--- a/Lib/compiler/ast.py
+++ b/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]]
diff --git a/Lib/compiler/pycodegen.py b/Lib/compiler/pycodegen.py
index 292e859..ef5a0d3 100644
--- a/Lib/compiler/pycodegen.py
+++ b/Lib/compiler/pycodegen.py
@@ -619,6 +619,79 @@ class CodeGenerator:
         self.newBlock()
         self.emit('POP_TOP')
 
+    def visitGenExpr(self, node):
+        gen = GenExprCodeGenerator(node, self.scopes, self.class_name,
+                                   self.get_module())
+        walk(node.code, gen)
+        gen.finish()
+        self.set_lineno(node)
+        frees = gen.scope.get_free_vars()
+        if frees:
+            for name in frees:
+                self.emit('LOAD_CLOSURE', name)
+            self.emit('LOAD_CONST', gen)
+            self.emit('MAKE_CLOSURE', 0)
+        else:
+            self.emit('LOAD_CONST', gen)
+            self.emit('MAKE_FUNCTION', 0)
+
+        # precomputation of outmost iterable
+        self.visit(node.code.quals[0].iter)
+        self.emit('GET_ITER')
+        self.emit('CALL_FUNCTION', 1)
+
+    def visitGenExprInner(self, node):
+        self.set_lineno(node)
+        # setup list
+
+        stack = []
+        for i, for_ in zip(range(len(node.quals)), node.quals):
+            start, anchor = self.visit(for_)
+            cont = None
+            for if_ in for_.ifs:
+                if cont is None:
+                    cont = self.newBlock()
+                self.visit(if_, cont)
+            stack.insert(0, (start, cont, anchor))
+
+        self.visit(node.expr)
+        self.emit('YIELD_VALUE')
+
+        for start, cont, anchor in stack:
+            if cont:
+                skip_one = self.newBlock()
+                self.emit('JUMP_FORWARD', skip_one)
+                self.startBlock(cont)
+                self.emit('POP_TOP')
+                self.nextBlock(skip_one)
+            self.emit('JUMP_ABSOLUTE', start)
+            self.startBlock(anchor)
+        self.emit('LOAD_CONST', None)
+
+    def visitGenExprFor(self, node):
+        start = self.newBlock()
+        anchor = self.newBlock()
+        
+        if node.is_outmost:
+            self.loadName('[outmost-iterable]')
+        else:
+            self.visit(node.iter)
+            self.emit('GET_ITER')
+
+        self.nextBlock(start)
+        self.set_lineno(node, force=True)
+        self.emit('FOR_ITER', anchor)
+        self.nextBlock()
+        self.visit(node.assign)
+        return start, anchor
+
+    def visitGenExprIf(self, node, branch):
+        self.set_lineno(node, force=True)
+        self.visit(node.test)
+        self.emit('JUMP_IF_FALSE', branch)
+        self.newBlock()
+        self.emit('POP_TOP')
+
     # exception related
 
     def visitAssert(self, node):
@@ -1199,6 +1272,7 @@ class AbstractFunctionCode:
             klass.lambdaCount = klass.lambdaCount + 1
         else:
             name = func.name
+
         args, hasTupleArg = generateArgList(func.argnames)
         self.graph = pyassem.PyFlowGraph(name, func.filename, args,
                                          optimized=1)
@@ -1263,6 +1337,21 @@ class FunctionCodeGenerator(NestedScopeMixin, AbstractFunctionCode,
         if self.scope.generator is not None:
             self.graph.setFlag(CO_GENERATOR)
 
+class GenExprCodeGenerator(NestedScopeMixin, AbstractFunctionCode,
+                           CodeGenerator):
+    super_init = CodeGenerator.__init__ # call be other init
+    scopes = None
+
+    __super_init = AbstractFunctionCode.__init__
+
+    def __init__(self, gexp, scopes, class_name, mod):
+        self.scopes = scopes
+        self.scope = scopes[gexp]
+        self.__super_init(gexp, scopes, 1, class_name, mod)
+        self.graph.setFreeVars(self.scope.get_free_vars())
+        self.graph.setCellVars(self.scope.get_cell_vars())
+        self.graph.setFlag(CO_GENERATOR)
+
 class AbstractClassCode:
 
     def __init__(self, klass, scopes, module):
diff --git a/Lib/compiler/symbols.py b/Lib/compiler/symbols.py
index fa668f1..6843e19 100644
--- a/Lib/compiler/symbols.py
+++ b/Lib/compiler/symbols.py
@@ -179,6 +179,21 @@ class ModuleScope(Scope):
 class FunctionScope(Scope):
     pass
 
+class GenExprScope(Scope):
+    __super_init = Scope.__init__
+
+    __counter = 1
+
+    def __init__(self, module, klass=None):
+        i = self.__counter
+        self.__counter += 1
+        self.__super_init("generator expression<%d>"%i, module, klass)
+        self.add_param('[outmost-iterable]')
+
+    def get_names(self):
+        keys = Scope.get_names()
+        return keys
+
 class LambdaScope(FunctionScope):
     __super_init = Scope.__init__
 
@@ -220,6 +235,32 @@ class SymbolVisitor:
         self.visit(node.code, scope)
         self.handle_free_vars(scope, parent)
 
+    def visitGenExpr(self, node, parent):
+        scope = GenExprScope(self.module, self.klass);
+        if parent.nested or isinstance(parent, FunctionScope) \
+                or isinstance(parent, GenExprScope):
+            scope.nested = 1
+
+        self.scopes[node] = scope
+        self.visit(node.code, scope)
+
+        self.handle_free_vars(scope, parent)
+
+    def visitGenExprInner(self, node, scope):
+        for genfor in node.quals:
+            self.visit(genfor, scope)
+
+        self.visit(node.expr, scope)
+
+    def visitGenExprFor(self, node, scope):
+        self.visit(node.assign, scope, 1)
+        self.visit(node.iter, scope)
+        for if_ in node.ifs:
+            self.visit(if_, scope)
+
+    def visitGenExprIf(self, node, scope):
+        self.visit(node.test, scope)
+        
     def visitLambda(self, node, parent, assign=0):
         # Lambda is an expression, so it could appear in an expression
         # context where assign is passed.  The transformer should catch
diff --git a/Lib/compiler/transformer.py b/Lib/compiler/transformer.py
index 9074fc7..6832cf1 100644
--- a/Lib/compiler/transformer.py
+++ b/Lib/compiler/transformer.py
@@ -534,6 +534,12 @@ class Transformer:
     testlist1 = testlist
     exprlist = testlist
 
+    def testlist_gexp(self, nodelist):
+        if len(nodelist) == 2 and nodelist[1][0] == symbol.gen_for:
+            test = self.com_node(nodelist[0])
+            return self.com_generator_expression(test, nodelist[1])
+        return self.testlist(nodelist)
+
     def test(self, nodelist):
         # and_test ('or' and_test)* | lambdef
         if len(nodelist) == 1 and nodelist[0][0] == symbol.lambdef:
@@ -1085,6 +1091,48 @@ class Transformer:
                 values.append(self.com_node(nodelist[i]))
             return List(values)
 
+    if hasattr(symbol, 'gen_for'):
+        def com_generator_expression(self, expr, node):
+            # gen_iter: gen_for | gen_if
+            # gen_for: 'for' exprlist 'in' test [gen_iter]
+            # gen_if: 'if' test [gen_iter]
+
+            lineno = node[1][2]
+            fors = []
+            while node:
+                t = node[1][1]
+                if t == 'for':
+                    assignNode = self.com_assign(node[2], OP_ASSIGN)
+                    genNode = self.com_node(node[4])
+                    newfor = GenExprFor(assignNode, genNode, [])
+                    newfor.lineno = node[1][2]
+                    fors.append(newfor)
+                    if (len(node)) == 5:
+                        node = None
+                    else:
+                        node = self.com_gen_iter(node[5])
+                elif t == 'if':
+                    test = self.com_node(node[2])
+                    newif = GenExprIf(test)
+                    newif.lineno = node[1][2]
+                    newfor.ifs.append(newif)
+                    if len(node) == 3:
+                        node = None
+                    else:
+                        node = self.com_gen_iter(node[3])
+                else:
+                    raise SyntaxError, \
+                            ("unexpected generator expression element: %s %d"
+                             % (node, lineno))
+            fors[0].is_outmost = True
+            n = GenExpr(GenExprInner(expr, fors))
+            n.lineno = lineno
+            return n
+
+        def com_gen_iter(self, node):
+            assert node[0] == symbol.gen_iter
+            return node[1]
+
     def com_dictmaker(self, nodelist):
         # dictmaker: test ':' test (',' test ':' value)* [',']
         items = []
@@ -1122,6 +1170,8 @@ class Transformer:
             if node[0] == token.STAR or node[0] == token.DOUBLESTAR:
                 break
             kw, result = self.com_argument(node, kw)
+            if len_nodelist != 2 and isinstance(result, GenExpr):
+                raise SyntaxError, 'generator expression needs parenthesis'
             args.append(result)
         else:
             # No broken by star arg, so skip the last one we processed.
@@ -1148,6 +1198,9 @@ class Transformer:
         return CallFunc(primaryNode, args, star_node, dstar_node)
 
     def com_argument(self, nodelist, kw):
+        if len(nodelist) == 3 and nodelist[2][0] == symbol.gen_for:
+            test = self.com_node(nodelist[1])
+            return 0, self.com_generator_expression(test, nodelist[2])
         if len(nodelist) == 2:
             if kw:
                 raise SyntaxError, "non-keyword arg after keyword arg"
diff --git a/Lib/symbol.py b/Lib/symbol.py
index 38c6193..c839e4a 100755
--- a/Lib/symbol.py
+++ b/Lib/symbol.py
@@ -61,23 +61,27 @@ factor = 303
 power = 304
 atom = 305
 listmaker = 306
-lambdef = 307
-trailer = 308
-subscriptlist = 309
-subscript = 310
-sliceop = 311
-exprlist = 312
-testlist = 313
-testlist_safe = 314
-dictmaker = 315
-classdef = 316
-arglist = 317
-argument = 318
-list_iter = 319
-list_for = 320
-list_if = 321
-testlist1 = 322
-encoding_decl = 323
+testlist_gexp = 307
+lambdef = 308
+trailer = 309
+subscriptlist = 310
+subscript = 311
+sliceop = 312
+exprlist = 313
+testlist = 314
+testlist_safe = 315
+dictmaker = 316
+classdef = 317
+arglist = 318
+argument = 319
+list_iter = 320
+list_for = 321
+list_if = 322
+gen_iter = 323
+gen_for = 324
+gen_if = 325
+testlist1 = 326
+encoding_decl = 327
 #--end constants--
 
 sym_name = {}
diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
index 9b857c5..bad8857 100644
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -566,7 +566,7 @@ def test_main(verbose=None):
 
     # doctests
     from test import test_deque
-#    test_support.run_doctest(test_deque, verbose)
+    test_support.run_doctest(test_deque, verbose)
 
 if __name__ == "__main__":
     test_main(verbose=True)
diff --git a/Lib/test/test_genexps.py b/Lib/test/test_genexps.py
new file mode 100644
index 0000000..b09fc95
--- /dev/null
+++ b/Lib/test/test_genexps.py
@@ -0,0 +1,258 @@
+doctests = """
+
+Test simple loop with conditional
+
+    >>> sum(i*i for i in range(100) if i&1 == 1)
+    166650
+
+Test simple nesting
+
+    >>> list((i,j) for i in range(3) for j in range(4) )
+    [(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]
+
+Test nesting with the inner expression dependent on the outer
+
+    >>> list((i,j) for i in range(4) for j in range(i) )
+    [(1, 0), (2, 0), (2, 1), (3, 0), (3, 1), (3, 2)]
+
+Make sure the induction variable is not exposed
+
+    >>> i = 20
+    >>> sum(i*i for i in range(100))
+    328350
+    >>> i
+    20
+
+Test first class
+
+    >>> g = (i*i for i in range(4))
+    >>> type(g)
+    <type 'generator'>
+    >>> list(g)
+    [0, 1, 4, 9]
+
+Test direct calls to next()
+
+    >>> g = (i*i for i in range(3))
+    >>> g.next()
+    0
+    >>> g.next()
+    1
+    >>> g.next()
+    4
+    >>> g.next()
+    Traceback (most recent call last):
+      File "<pyshell#21>", line 1, in -toplevel-
+        g.next()
+    StopIteration
+
+Does it stay stopped?
+
+    >>> g.next()
+    Traceback (most recent call last):
+      File "<pyshell#21>", line 1, in -toplevel-
+        g.next()
+    StopIteration
+    >>> list(g)
+    []
+
+Test running gen when defining function is out of scope
+
+    >>> def f(n):
+    ...     return (i*i for i in xrange(n))
+    ...
+    >>> list(f(10))
+    [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
+
+    >>> def f(n):
+    ...     return ((i,j) for i in xrange(3) for j in xrange(n))
+    ...
+    >>> list(f(4))
+    [(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]
+    >>> def f(n):
+    ...     return ((i,j) for i in xrange(3) for j in xrange(4) if j in xrange(n))
+    ...
+    >>> list(f(4))
+    [(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]
+    >>> list(f(2))
+    [(0, 0), (0, 1), (1, 0), (1, 1), (2, 0), (2, 1)]
+
+#Verify that parenthesis are required in a statement
+#>>> def f(n):
+#...     return i*i for i in xrange(n)
+#...
+#SyntaxError: invalid syntax
+
+Verify early binding for the outermost for-expression
+
+    >>> x=10
+    >>> g = (i*i for i in range(x))
+    >>> x = 5
+    >>> list(g)
+    [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
+
+Verify late binding for the outermost if-expression
+
+    >>> include = (2,4,6,8)
+    >>> g = (i*i for i in range(10) if i in include)
+    >>> include = (1,3,5,7,9)
+    >>> list(g)
+    [1, 9, 25, 49, 81]
+
+Verify late binding for the innermost for-expression
+
+    >>> g = ((i,j) for i in range(3) for j in range(x))
+    >>> x = 4
+    >>> list(g)
+    [(0, 0), (0, 1), (0, 2), (0, 3), (1, 0), (1, 1), (1, 2), (1, 3), (2, 0), (2, 1), (2, 2), (2, 3)]
+
+Verify re-use of tuples (a side benefit of using genexps over listcomps)
+
+    >>> tupleids = map(id, ((i,i) for i in xrange(10)))
+    >>> max(tupleids) - min(tupleids)
+    0
+
+
+
+########### Tests borrowed from or inspired by test_generators.py ############
+
+Make a generator that acts like range()
+
+    >>> yrange = lambda n:  (i for i in xrange(n))
+    >>> list(yrange(10))
+    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+
+Generators always return to the most recent caller:
+
+    >>> def creator():
+    ...     r = yrange(5)
+    ...     print "creator", r.next()
+    ...     return r
+    ...
+    >>> def caller():
+    ...     r = creator()
+    ...     for i in r:
+    ...             print "caller", i
+    ...
+    >>> caller()
+    creator 0
+    caller 1
+    caller 2
+    caller 3
+    caller 4
+
+Generators can call other generators:
+
+    >>> def zrange(n):
+    ...     for i in yrange(n):
+    ...         yield i
+    ...
+    >>> list(zrange(5))
+    [0, 1, 2, 3, 4]
+
+
+Verify that a gen exp cannot be resumed while it is actively running:
+
+    >>> g = (me.next() for i in xrange(10))
+    >>> me = g
+    >>> me.next()
+    Traceback (most recent call last):
+      File "<pyshell#30>", line 1, in -toplevel-
+        me.next()
+      File "<pyshell#28>", line 1, in <generator expression>
+        g = (me.next() for i in xrange(10))
+    ValueError: generator already executing
+
+Verify exception propagation
+
+    >>> g = (10 // i for i in (5, 0, 2))
+    >>> g.next()
+    2
+    >>> g.next()
+    Traceback (most recent call last):
+      File "<pyshell#37>", line 1, in -toplevel-
+        g.next()
+      File "<pyshell#35>", line 1, in <generator expression>
+        g = (10 // i for i in (5, 0, 2))
+    ZeroDivisionError: integer division or modulo by zero
+    >>> g.next()
+    Traceback (most recent call last):
+      File "<pyshell#38>", line 1, in -toplevel-
+        g.next()
+    StopIteration
+
+Make sure that None is a valid return value
+
+    >>> list(None for i in xrange(10))
+    [None, None, None, None, None, None, None, None, None, None]
+
+Check that generator attributes are present
+
+    >>> g = (i*i for i in range(3))
+    >>> expected = set(['gi_frame', 'gi_running', 'next'])
+    >>> set(attr for attr in dir(g) if not attr.startswith('__')) >= expected
+    True
+
+    >>> print g.next.__doc__
+    x.next() -> the next value, or raise StopIteration
+    >>> import types
+    >>> isinstance(g, types.GeneratorType)
+    True
+
+Check the __iter__ slot is defined to return self
+
+    >>> iter(g) is g
+    True
+
+Verify that the running flag is set properly
+
+    >>> g = (me.gi_running for i in (0,1))
+    >>> me = g
+    >>> me.gi_running
+    0
+    >>> me.next()
+    1
+    >>> me.gi_running
+    0
+
+Verify that genexps are weakly referencable
+
+    >>> import weakref
+    >>> g = (i*i for i in range(4))
+    >>> wr = weakref.ref(g)
+    >>> wr() is g
+    True
+    >>> p = weakref.proxy(g)
+    >>> list(p)
+    [0, 1, 4, 9]
+
+
+"""
+
+
+__test__ = {'doctests' : doctests}
+
+def test_main(verbose=None):
+    import sys
+    from test import test_support
+    from test import test_genexps
+    test_support.run_doctest(test_genexps, verbose)
+
+    # verify reference counting
+    if verbose and hasattr(sys, "gettotalrefcount"):
+        import gc
+        counts = [None] * 5
+        for i in xrange(len(counts)):
+            test_support.run_doctest(test_genexps, verbose)
+            gc.collect()
+            counts[i] = sys.gettotalrefcount()
+        print counts
+
+if __name__ == "__main__":
+    test_main(verbose=True)
+
+
+
+
+
+
diff --git a/Lib/test/test_grammar.py b/Lib/test/test_grammar.py
index 0eed4bb..e0d5b74 100644
--- a/Lib/test/test_grammar.py
+++ b/Lib/test/test_grammar.py
@@ -739,3 +739,46 @@ print [
         for (sp_sno, sp_pno) in suppart
           if sno == sp_sno and pno == sp_pno
 ]
+
+# generator expression tests
+g = ([x for x in range(10)] for x in range(1))
+verify(g.next() == [x for x in range(10)])
+try:
+    g.next()
+    raise TestFailed, 'should produce StopIteration exception'
+except StopIteration:
+    pass
+
+a = 1
+try:
+    g = (a for d in a)
+    g.next()
+    raise TestFailed, 'should produce TypeError'
+except TypeError:
+    pass
+
+verify(list((x, y) for x in 'abcd' for y in 'abcd') == [(x, y) for x in 'abcd' for y in 'abcd'])
+verify(list((x, y) for x in 'ab' for y in 'xy') == [(x, y) for x in 'ab' for y in 'xy'])
+
+a = [x for x in range(10)]
+b = (x for x in (y for y in a))
+verify(sum(b) == sum([x for x in range(10)]))
+
+verify(sum(x**2 for x in range(10)) == sum([x**2 for x in range(10)]))
+verify(sum(x*x for x in range(10) if x%2) == sum([x*x for x in range(10) if x%2]))
+verify(sum(x for x in (y for y in range(10))) == sum([x for x in range(10)]))
+verify(sum(x for x in (y for y in (z for z in range(10)))) == sum([x for x in range(10)]))
+verify(sum(x for x in [y for y in (z for z in range(10))]) == sum([x for x in range(10)]))
+verify(sum(x for x in (y for y in (z for z in range(10) if True)) if True) == sum([x for x in range(10)]))
+verify(sum(x for x in (y for y in (z for z in range(10) if True) if False) if True) == 0)
+check_syntax("foo(x for x in range(10), 100)")
+check_syntax("foo(100, x for x in range(10))")
+
+# test for outmost iterable precomputation
+x = 10; g = (i for i in range(x)); x = 5
+verify(len(list(g)) == 10)
+
+# This should hold, since we're only precomputing outmost iterable.
+x = 10; t = False; g = ((i,j) for i in range(x) if t for j in range(x))
+x = 5; t = True;
+verify([(i,j) for i in range(10) for j in range(5)] == list(g))
diff --git a/Lib/test/test_parser.py b/Lib/test/test_parser.py
index 7860e7b..9652f6b 100644
--- a/Lib/test/test_parser.py
+++ b/Lib/test/test_parser.py
@@ -67,6 +67,8 @@ class RoundtripLegalSyntaxTestCase(unittest.TestCase):
         self.check_expr("lambda foo=bar, blaz=blat+2, **z: 0")
         self.check_expr("lambda foo=bar, blaz=blat+2, *y, **z: 0")
         self.check_expr("lambda x, *y, **z: 0")
+        self.check_expr("(x for x in range(10))")
+        self.check_expr("foo(x for x in range(10))")
 
     def test_print(self):
         self.check_suite("print")