PEP 448: additional unpacking generalizations (closes #2292)

Patch by Neil Girdhar.

8 files changed, 263 insertions, 41 deletions

diff --git a/Lib/importlib/_bootstrap_external.py b/Lib/importlib/_bootstrap_external.py
index 9385d112d2..b76c550e9d 100644
--- a/Lib/importlib/_bootstrap_external.py
+++ b/Lib/importlib/_bootstrap_external.py
@@ -220,12 +220,13 @@ _code_type = type(_write_atomic.__code__)
 #     Python 3.4a4  3300 (more changes to __qualname__ computation)
 #     Python 3.4rc2 3310 (alter __qualname__ computation)
 #     Python 3.5a0  3320 (matrix multiplication operator)
+#     Python 3.5b1  3330 (PEP 448: Additional Unpacking Generalizations)
 #
 # MAGIC must change whenever the bytecode emitted by the compiler may no
 # longer be understood by older implementations of the eval loop (usually
 # due to the addition of new opcodes).
 
-MAGIC_NUMBER = (3320).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3330).to_bytes(2, 'little') + b'\r\n'
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 
 _PYCACHE = '__pycache__'
diff --git a/Lib/opcode.py b/Lib/opcode.py
index bfd3c4d8dd..c25afd44a7 100644
--- a/Lib/opcode.py
+++ b/Lib/opcode.py
@@ -200,4 +200,10 @@ hasfree.append(148)
 def_op('EXTENDED_ARG', 144)
 EXTENDED_ARG = 144
 
+def_op('BUILD_LIST_UNPACK', 149)
+def_op('BUILD_MAP_UNPACK', 150)
+def_op('BUILD_MAP_UNPACK_WITH_CALL', 151)
+def_op('BUILD_TUPLE_UNPACK', 152)
+def_op('BUILD_SET_UNPACK', 153)
+
 del def_op, name_op, jrel_op, jabs_op
diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py
index a533f8693b..1d9de2c4b5 100644
--- a/Lib/test/test_ast.py
+++ b/Lib/test/test_ast.py
@@ -427,17 +427,17 @@ class ASTHelpers_Test(unittest.TestCase):
         self.assertEqual(ast.dump(node),
             "Module(body=[Expr(value=Call(func=Name(id='spam', ctx=Load()), "
             "args=[Name(id='eggs', ctx=Load()), Str(s='and cheese')], "
-            "keywords=[], starargs=None, kwargs=None))])"
+            "keywords=[]))])"
         )
         self.assertEqual(ast.dump(node, annotate_fields=False),
             "Module([Expr(Call(Name('spam', Load()), [Name('eggs', Load()), "
-            "Str('and cheese')], [], None, None))])"
+            "Str('and cheese')], []))])"
         )
         self.assertEqual(ast.dump(node, include_attributes=True),
             "Module(body=[Expr(value=Call(func=Name(id='spam', ctx=Load(), "
             "lineno=1, col_offset=0), args=[Name(id='eggs', ctx=Load(), "
             "lineno=1, col_offset=5), Str(s='and cheese', lineno=1, "
-            "col_offset=11)], keywords=[], starargs=None, kwargs=None, "
+            "col_offset=11)], keywords=[], "
             "lineno=1, col_offset=0), lineno=1, col_offset=0)])"
         )
 
@@ -453,16 +453,16 @@ class ASTHelpers_Test(unittest.TestCase):
     def test_fix_missing_locations(self):
         src = ast.parse('write("spam")')
         src.body.append(ast.Expr(ast.Call(ast.Name('spam', ast.Load()),
-                                          [ast.Str('eggs')], [], None, None)))
+                                          [ast.Str('eggs')], [])))
         self.assertEqual(src, ast.fix_missing_locations(src))
         self.assertEqual(ast.dump(src, include_attributes=True),
             "Module(body=[Expr(value=Call(func=Name(id='write', ctx=Load(), "
             "lineno=1, col_offset=0), args=[Str(s='spam', lineno=1, "
-            "col_offset=6)], keywords=[], starargs=None, kwargs=None, "
+            "col_offset=6)], keywords=[], "
             "lineno=1, col_offset=0), lineno=1, col_offset=0), "
             "Expr(value=Call(func=Name(id='spam', ctx=Load(), lineno=1, "
             "col_offset=0), args=[Str(s='eggs', lineno=1, col_offset=0)], "
-            "keywords=[], starargs=None, kwargs=None, lineno=1, "
+            "keywords=[], lineno=1, "
             "col_offset=0), lineno=1, col_offset=0)])"
         )
 
@@ -487,8 +487,7 @@ class ASTHelpers_Test(unittest.TestCase):
         node = ast.parse('foo()', mode='eval')
         d = dict(ast.iter_fields(node.body))
         self.assertEqual(d.pop('func').id, 'foo')
-        self.assertEqual(d, {'keywords': [], 'kwargs': None,
-                             'args': [], 'starargs': None})
+        self.assertEqual(d, {'keywords': [], 'args': []})
 
     def test_iter_child_nodes(self):
         node = ast.parse("spam(23, 42, eggs='leek')", mode='eval')
@@ -604,8 +603,7 @@ class ASTValidatorTests(unittest.TestCase):
         self._check_arguments(fac, self.stmt)
 
     def test_classdef(self):
-        def cls(bases=None, keywords=None, starargs=None, kwargs=None,
-                body=None, decorator_list=None):
+        def cls(bases=None, keywords=None, body=None, decorator_list=None):
             if bases is None:
                 bases = []
             if keywords is None:
@@ -614,16 +612,12 @@ class ASTValidatorTests(unittest.TestCase):
                 body = [ast.Pass()]
             if decorator_list is None:
                 decorator_list = []
-            return ast.ClassDef("myclass", bases, keywords, starargs,
-                                kwargs, body, decorator_list)
+            return ast.ClassDef("myclass", bases, keywords,
+                                body, decorator_list)
         self.stmt(cls(bases=[ast.Name("x", ast.Store())]),
                   "must have Load context")
         self.stmt(cls(keywords=[ast.keyword("x", ast.Name("x", ast.Store()))]),
                   "must have Load context")
-        self.stmt(cls(starargs=ast.Name("x", ast.Store())),
-                  "must have Load context")
-        self.stmt(cls(kwargs=ast.Name("x", ast.Store())),
-                  "must have Load context")
         self.stmt(cls(body=[]), "empty body on ClassDef")
         self.stmt(cls(body=[None]), "None disallowed")
         self.stmt(cls(decorator_list=[ast.Name("x", ast.Store())]),
@@ -854,20 +848,12 @@ class ASTValidatorTests(unittest.TestCase):
         func = ast.Name("x", ast.Load())
         args = [ast.Name("y", ast.Load())]
         keywords = [ast.keyword("w", ast.Name("z", ast.Load()))]
-        stararg = ast.Name("p", ast.Load())
-        kwarg = ast.Name("q", ast.Load())
-        call = ast.Call(ast.Name("x", ast.Store()), args, keywords, stararg,
-                        kwarg)
+        call = ast.Call(ast.Name("x", ast.Store()), args, keywords)
         self.expr(call, "must have Load context")
-        call = ast.Call(func, [None], keywords, stararg, kwarg)
+        call = ast.Call(func, [None], keywords)
         self.expr(call, "None disallowed")
         bad_keywords = [ast.keyword("w", ast.Name("z", ast.Store()))]
-        call = ast.Call(func, args, bad_keywords, stararg, kwarg)
-        self.expr(call, "must have Load context")
-        call = ast.Call(func, args, keywords, ast.Name("z", ast.Store()), kwarg)
-        self.expr(call, "must have Load context")
-        call = ast.Call(func, args, keywords, stararg,
-                        ast.Name("w", ast.Store()))
+        call = ast.Call(func, args, bad_keywords)
         self.expr(call, "must have Load context")
 
     def test_num(self):
@@ -957,8 +943,8 @@ exec_results = [
 ('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [], ('arg', (1, 7), 'args', None), [], [], None, []), [('Pass', (1, 14))], [], None)]),
 ('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], ('arg', (1, 8), 'kwargs', None), []), [('Pass', (1, 17))], [], None)]),
 ('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [('arg', (1, 6), 'a', None), ('arg', (1, 9), 'b', None), ('arg', (1, 14), 'c', None), ('arg', (1, 22), 'd', None), ('arg', (1, 28), 'e', None)], ('arg', (1, 35), 'args', None), [('arg', (1, 41), 'f', None)], [('Num', (1, 43), 42)], ('arg', (1, 49), 'kwargs', None), [('Num', (1, 11), 1), ('NameConstant', (1, 16), None), ('List', (1, 24), [], ('Load',)), ('Dict', (1, 30), [], [])]), [('Pass', (1, 58))], [], None)]),
-('Module', [('ClassDef', (1, 0), 'C', [], [], None, None, [('Pass', (1, 8))], [])]),
-('Module', [('ClassDef', (1, 0), 'C', [('Name', (1, 8), 'object', ('Load',))], [], None, None, [('Pass', (1, 17))], [])]),
+('Module', [('ClassDef', (1, 0), 'C', [], [], [('Pass', (1, 8))], [])]),
+('Module', [('ClassDef', (1, 0), 'C', [('Name', (1, 8), 'object', ('Load',))], [], [('Pass', (1, 17))], [])]),
 ('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('Return', (1, 8), ('Num', (1, 15), 1))], [], None)]),
 ('Module', [('Delete', (1, 0), [('Name', (1, 4), 'v', ('Del',))])]),
 ('Module', [('Assign', (1, 0), [('Name', (1, 0), 'v', ('Store',))], ('Num', (1, 4), 1))]),
@@ -968,7 +954,7 @@ exec_results = [
 ('Module', [('If', (1, 0), ('Name', (1, 3), 'v', ('Load',)), [('Pass', (1, 5))], [])]),
 ('Module', [('With', (1, 0), [('withitem', ('Name', (1, 5), 'x', ('Load',)), ('Name', (1, 10), 'y', ('Store',)))], [('Pass', (1, 13))])]),
 ('Module', [('With', (1, 0), [('withitem', ('Name', (1, 5), 'x', ('Load',)), ('Name', (1, 10), 'y', ('Store',))), ('withitem', ('Name', (1, 13), 'z', ('Load',)), ('Name', (1, 18), 'q', ('Store',)))], [('Pass', (1, 21))])]),
-('Module', [('Raise', (1, 0), ('Call', (1, 6), ('Name', (1, 6), 'Exception', ('Load',)), [('Str', (1, 16), 'string')], [], None, None), None)]),
+('Module', [('Raise', (1, 0), ('Call', (1, 6), ('Name', (1, 6), 'Exception', ('Load',)), [('Str', (1, 16), 'string')], []), None)]),
 ('Module', [('Try', (1, 0), [('Pass', (2, 2))], [('ExceptHandler', (3, 0), ('Name', (3, 7), 'Exception', ('Load',)), None, [('Pass', (4, 2))])], [], [])]),
 ('Module', [('Try', (1, 0), [('Pass', (2, 2))], [], [], [('Pass', (4, 2))])]),
 ('Module', [('Assert', (1, 0), ('Name', (1, 7), 'v', ('Load',)), None)]),
@@ -998,14 +984,14 @@ eval_results = [
 ('Expression', ('BinOp', (1, 0), ('Name', (1, 0), 'a', ('Load',)), ('Add',), ('Name', (1, 4), 'b', ('Load',)))),
 ('Expression', ('UnaryOp', (1, 0), ('Not',), ('Name', (1, 4), 'v', ('Load',)))),
 ('Expression', ('Lambda', (1, 0), ('arguments', [], None, [], [], None, []), ('NameConstant', (1, 7), None))),
-('Expression', ('Dict', (1, 0), [('Num', (1, 2), 1)], [('Num', (1, 4), 2)])),
+('Expression', ('Dict', (1, 2), [('Num', (1, 2), 1)], [('Num', (1, 4), 2)])),
 ('Expression', ('Dict', (1, 0), [], [])),
-('Expression', ('Set', (1, 0), [('NameConstant', (1, 1), None)])),
-('Expression', ('Dict', (1, 0), [('Num', (2, 6), 1)], [('Num', (4, 10), 2)])),
+('Expression', ('Set', (1, 1), [('NameConstant', (1, 1), None)])),
+('Expression', ('Dict', (2, 6), [('Num', (2, 6), 1)], [('Num', (4, 10), 2)])),
 ('Expression', ('ListComp', (1, 1), ('Name', (1, 1), 'a', ('Load',)), [('comprehension', ('Name', (1, 7), 'b', ('Store',)), ('Name', (1, 12), 'c', ('Load',)), [('Name', (1, 17), 'd', ('Load',))])])),
 ('Expression', ('GeneratorExp', (1, 1), ('Name', (1, 1), 'a', ('Load',)), [('comprehension', ('Name', (1, 7), 'b', ('Store',)), ('Name', (1, 12), 'c', ('Load',)), [('Name', (1, 17), 'd', ('Load',))])])),
 ('Expression', ('Compare', (1, 0), ('Num', (1, 0), 1), [('Lt',), ('Lt',)], [('Num', (1, 4), 2), ('Num', (1, 8), 3)])),
-('Expression', ('Call', (1, 0), ('Name', (1, 0), 'f', ('Load',)), [('Num', (1, 2), 1), ('Num', (1, 4), 2)], [('keyword', 'c', ('Num', (1, 8), 3))], ('Name', (1, 11), 'd', ('Load',)), ('Name', (1, 15), 'e', ('Load',)))),
+('Expression', ('Call', (1, 0), ('Name', (1, 0), 'f', ('Load',)), [('Num', (1, 2), 1), ('Num', (1, 4), 2), ('Starred', (1, 10), ('Name', (1, 11), 'd', ('Load',)), ('Load',))], [('keyword', 'c', ('Num', (1, 8), 3)), ('keyword', None, ('Name', (1, 15), 'e', ('Load',)))])),
 ('Expression', ('Num', (1, 0), 10)),
 ('Expression', ('Str', (1, 0), 'string')),
 ('Expression', ('Attribute', (1, 0), ('Name', (1, 0), 'a', ('Load',)), 'b', ('Load',))),
@@ -1016,6 +1002,6 @@ eval_results = [
 ('Expression', ('Tuple', (1, 0), [('Num', (1, 0), 1), ('Num', (1, 2), 2), ('Num', (1, 4), 3)], ('Load',))),
 ('Expression', ('Tuple', (1, 1), [('Num', (1, 1), 1), ('Num', (1, 3), 2), ('Num', (1, 5), 3)], ('Load',))),
 ('Expression', ('Tuple', (1, 0), [], ('Load',))),
-('Expression', ('Call', (1, 0), ('Attribute', (1, 0), ('Attribute', (1, 0), ('Attribute', (1, 0), ('Name', (1, 0), 'a', ('Load',)), 'b', ('Load',)), 'c', ('Load',)), 'd', ('Load',)), [('Subscript', (1, 8), ('Attribute', (1, 8), ('Name', (1, 8), 'a', ('Load',)), 'b', ('Load',)), ('Slice', ('Num', (1, 12), 1), ('Num', (1, 14), 2), None), ('Load',))], [], None, None)),
+('Expression', ('Call', (1, 0), ('Attribute', (1, 0), ('Attribute', (1, 0), ('Attribute', (1, 0), ('Name', (1, 0), 'a', ('Load',)), 'b', ('Load',)), 'c', ('Load',)), 'd', ('Load',)), [('Subscript', (1, 8), ('Attribute', (1, 8), ('Name', (1, 8), 'a', ('Load',)), 'b', ('Load',)), ('Slice', ('Num', (1, 12), 1), ('Num', (1, 14), 2), None), ('Load',))], [])),
 ]
 main()
diff --git a/Lib/test/test_extcall.py b/Lib/test/test_extcall.py
index 6b6c12de2e..654258eb24 100644
--- a/Lib/test/test_extcall.py
+++ b/Lib/test/test_extcall.py
@@ -34,17 +34,37 @@ Argument list examples
     (1, 2, 3, 4, 5) {}
     >>> f(1, 2, 3, *[4, 5])
     (1, 2, 3, 4, 5) {}
+    >>> f(*[1, 2, 3], 4, 5)
+    (1, 2, 3, 4, 5) {}
     >>> f(1, 2, 3, *UserList([4, 5]))
     (1, 2, 3, 4, 5) {}
+    >>> f(1, 2, 3, *[4, 5], *[6, 7])
+    (1, 2, 3, 4, 5, 6, 7) {}
+    >>> f(1, *[2, 3], 4, *[5, 6], 7)
+    (1, 2, 3, 4, 5, 6, 7) {}
+    >>> f(*UserList([1, 2]), *UserList([3, 4]), 5, *UserList([6, 7]))
+    (1, 2, 3, 4, 5, 6, 7) {}
 
 Here we add keyword arguments
 
     >>> f(1, 2, 3, **{'a':4, 'b':5})
     (1, 2, 3) {'a': 4, 'b': 5}
+    >>> f(1, 2, **{'a': -1, 'b': 5}, **{'a': 4, 'c': 6})
+    Traceback (most recent call last):
+        ...
+    TypeError: f() got multiple values for keyword argument 'a'
+    >>> f(1, 2, **{'a': -1, 'b': 5}, a=4, c=6)
+    Traceback (most recent call last):
+        ...
+    TypeError: f() got multiple values for keyword argument 'a'
     >>> f(1, 2, 3, *[4, 5], **{'a':6, 'b':7})
     (1, 2, 3, 4, 5) {'a': 6, 'b': 7}
     >>> f(1, 2, 3, x=4, y=5, *(6, 7), **{'a':8, 'b': 9})
     (1, 2, 3, 6, 7) {'a': 8, 'b': 9, 'x': 4, 'y': 5}
+    >>> f(1, 2, 3, *[4, 5], **{'c': 8}, **{'a':6, 'b':7})
+    (1, 2, 3, 4, 5) {'a': 6, 'b': 7, 'c': 8}
+    >>> f(1, 2, 3, *(4, 5), x=6, y=7, **{'a':8, 'b': 9})
+    (1, 2, 3, 4, 5) {'a': 8, 'b': 9, 'x': 6, 'y': 7}
 
     >>> f(1, 2, 3, **UserDict(a=4, b=5))
     (1, 2, 3) {'a': 4, 'b': 5}
@@ -52,6 +72,8 @@ Here we add keyword arguments
     (1, 2, 3, 4, 5) {'a': 6, 'b': 7}
     >>> f(1, 2, 3, x=4, y=5, *(6, 7), **UserDict(a=8, b=9))
     (1, 2, 3, 6, 7) {'a': 8, 'b': 9, 'x': 4, 'y': 5}
+    >>> f(1, 2, 3, *(4, 5), x=6, y=7, **UserDict(a=8, b=9))
+    (1, 2, 3, 4, 5) {'a': 8, 'b': 9, 'x': 6, 'y': 7}
 
 Examples with invalid arguments (TypeErrors). We're also testing the function
 names in the exception messages.
diff --git a/Lib/test/test_grammar.py b/Lib/test/test_grammar.py
index 0c658587e9..28b1f044f2 100644
--- a/Lib/test/test_grammar.py
+++ b/Lib/test/test_grammar.py
@@ -296,8 +296,12 @@ class GrammarTests(unittest.TestCase):
             return args, kwargs
         self.assertEqual(f(1, x=2, *[3, 4], y=5), ((1, 3, 4),
                                                     {'x':2, 'y':5}))
-        self.assertRaises(SyntaxError, eval, "f(1, *(2,3), 4)")
+        self.assertEqual(f(1, *(2,3), 4), ((1, 2, 3, 4), {}))
         self.assertRaises(SyntaxError, eval, "f(1, x=2, *(3,4), x=5)")
+        self.assertEqual(f(**{'eggs':'scrambled', 'spam':'fried'}),
+                         ((), {'eggs':'scrambled', 'spam':'fried'}))
+        self.assertEqual(f(spam='fried', **{'eggs':'scrambled'}),
+                         ((), {'eggs':'scrambled', 'spam':'fried'}))
 
         # argument annotation tests
         def f(x) -> list: pass
diff --git a/Lib/test/test_parser.py b/Lib/test/test_parser.py
index 2112821237..18f16e3f52 100644
--- a/Lib/test/test_parser.py
+++ b/Lib/test/test_parser.py
@@ -313,7 +313,12 @@ class RoundtripLegalSyntaxTestCase(unittest.TestCase):
                          "except Exception as e:\n"
                          "    raise ValueError from e\n")
 
+    def test_list_displays(self):
+        self.check_expr('[]')
+        self.check_expr('[*{2}, 3, *[4]]')
+
     def test_set_displays(self):
+        self.check_expr('{*{2}, 3, *[4]}')
         self.check_expr('{2}')
         self.check_expr('{2,}')
         self.check_expr('{2, 3}')
@@ -325,6 +330,13 @@ class RoundtripLegalSyntaxTestCase(unittest.TestCase):
         self.check_expr('{a:b,}')
         self.check_expr('{a:b, c:d}')
         self.check_expr('{a:b, c:d,}')
+        self.check_expr('{**{}}')
+        self.check_expr('{**{}, 3:4, **{5:6, 7:8}}')
+
+    def test_argument_unpacking(self):
+        self.check_expr('f(a, *b, *c, *d)')
+        self.check_expr('f(**a, **b)')
+        self.check_expr('f(2, *a, *b, **b, **c, **d)')
 
     def test_set_comprehensions(self):
         self.check_expr('{x for x in seq}')
diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
index a9d3628819..a22cebb828 100644
--- a/Lib/test/test_syntax.py
+++ b/Lib/test/test_syntax.py
@@ -141,6 +141,9 @@ From ast_for_call():
 >>> f(x for x in L, 1)
 Traceback (most recent call last):
 SyntaxError: Generator expression must be parenthesized if not sole argument
+>>> f(x for x in L, y for y in L)
+Traceback (most recent call last):
+SyntaxError: Generator expression must be parenthesized if not sole argument
 >>> f((x for x in L), 1)
 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
 
@@ -582,7 +585,18 @@ class SyntaxTestCase(unittest.TestCase):
                           subclass=IndentationError)
 
     def test_kwargs_last(self):
-        self._check_error("int(base=10, '2')", "non-keyword arg")
+        self._check_error("int(base=10, '2')",
+                          "positional argument follows keyword argument")
+
+    def test_kwargs_last2(self):
+        self._check_error("int(**{base: 10}, '2')",
+                          "positional argument follows "
+                          "keyword argument unpacking")
+
+    def test_kwargs_last3(self):
+        self._check_error("int(**{base: 10}, *['2'])",
+                          "iterable argument unpacking follows "
+                          "keyword argument unpacking")
 
 def test_main():
     support.run_unittest(SyntaxTestCase)
diff --git a/Lib/test/test_unpack_ex.py b/Lib/test/test_unpack_ex.py
index 54666b0cf0..01f57b95e7 100644
--- a/Lib/test/test_unpack_ex.py
+++ b/Lib/test/test_unpack_ex.py
@@ -71,8 +71,185 @@ Multiple targets
     >>> a == 0 and b == [1, 2, 3] and c == 4 and d == [0, 1, 2, 3] and e == 4
     True
 
+Assignment unpacking
+
+    >>> a, b, *c = range(5)
+    >>> a, b, c
+    (0, 1, [2, 3, 4])
+    >>> *a, b, c = a, b, *c
+    >>> a, b, c
+    ([0, 1, 2], 3, 4)
+
+Set display element unpacking
+
+    >>> a = [1, 2, 3]
+    >>> sorted({1, *a, 0, 4})
+    [0, 1, 2, 3, 4]
+
+    >>> {1, *1, 0, 4}
+    Traceback (most recent call last):
+      ...
+    TypeError: 'int' object is not iterable
+
+Dict display element unpacking
+
+    >>> kwds = {'z': 0, 'w': 12}
+    >>> sorted({'x': 1, 'y': 2, **kwds}.items())
+    [('w', 12), ('x', 1), ('y', 2), ('z', 0)]
+
+    >>> sorted({**{'x': 1}, 'y': 2, **{'z': 3}}.items())
+    [('x', 1), ('y', 2), ('z', 3)]
+
+    >>> sorted({**{'x': 1}, 'y': 2, **{'x': 3}}.items())
+    [('x', 3), ('y', 2)]
+
+    >>> sorted({**{'x': 1}, **{'x': 3}, 'x': 4}.items())
+    [('x', 4)]
+
+    >>> {**{}}
+    {}
+
+    >>> a = {}
+    >>> {**a}[0] = 1
+    >>> a
+    {}
+
+    >>> {**1}
+    Traceback (most recent call last):
+    ...
+    TypeError: 'int' object is not a mapping
+
+    >>> {**[]}
+    Traceback (most recent call last):
+    ...
+    TypeError: 'list' object is not a mapping
+
+    >>> len(eval("{" + ", ".join("**{{{}: {}}}".format(i, i)
+    ...                          for i in range(1000)) + "}"))
+    1000
+
+List comprehension element unpacking
+
+    >>> a, b, c = [0, 1, 2], 3, 4
+    >>> [*a, b, c]
+    [0, 1, 2, 3, 4]
+
+    >>> l = [a, (3, 4), {5}, {6: None}, (i for i in range(7, 10))]
+    >>> [*item for item in l]
+    Traceback (most recent call last):
+    ...
+    SyntaxError: iterable unpacking cannot be used in comprehension
+
+    >>> [*[0, 1] for i in range(10)]
+    Traceback (most recent call last):
+    ...
+    SyntaxError: iterable unpacking cannot be used in comprehension
+
+    >>> [*'a' for i in range(10)]
+    Traceback (most recent call last):
+    ...
+    SyntaxError: iterable unpacking cannot be used in comprehension
+
+    >>> [*[] for i in range(10)]
+    Traceback (most recent call last):
+    ...
+    SyntaxError: iterable unpacking cannot be used in comprehension
+
+Generator expression in function arguments
+
+    >>> list(*x for x in (range(5) for i in range(3)))
+    Traceback (most recent call last):
+    ...
+        list(*x for x in (range(5) for i in range(3)))
+                  ^
+    SyntaxError: invalid syntax
+
+    >>> dict(**x for x in [{1:2}])
+    Traceback (most recent call last):
+    ...
+        dict(**x for x in [{1:2}])
+                   ^
+    SyntaxError: invalid syntax
+
+Iterable argument unpacking
+
+    >>> print(*[1], *[2], 3)
+    1 2 3
+
+Make sure that they don't corrupt the passed-in dicts.
+
+    >>> def f(x, y):
+    ...     print(x, y)
+    ...
+    >>> original_dict = {'x': 1}
+    >>> f(**original_dict, y=2)
+    1 2
+    >>> original_dict
+    {'x': 1}
+
 Now for some failures
 
+Make sure the raised errors are right for keyword argument unpackings
+
+    >>> from collections.abc import MutableMapping
+    >>> class CrazyDict(MutableMapping):
+    ...     def __init__(self):
+    ...         self.d = {}
+    ...
+    ...     def __iter__(self):
+    ...         for x in self.d.__iter__():
+    ...             if x == 'c':
+    ...                 self.d['z'] = 10
+    ...             yield x
+    ...
+    ...     def __getitem__(self, k):
+    ...         return self.d[k]
+    ...
+    ...     def __len__(self):
+    ...         return len(self.d)
+    ...
+    ...     def __setitem__(self, k, v):
+    ...         self.d[k] = v
+    ...
+    ...     def __delitem__(self, k):
+    ...         del self.d[k]
+    ...
+    >>> d = CrazyDict()
+    >>> d.d = {chr(ord('a') + x): x for x in range(5)}
+    >>> e = {**d}
+    Traceback (most recent call last):
+    ...
+    RuntimeError: dictionary changed size during iteration
+
+    >>> d.d = {chr(ord('a') + x): x for x in range(5)}
+    >>> def f(**kwargs): print(kwargs)
+    >>> f(**d)
+    Traceback (most recent call last):
+    ...
+    RuntimeError: dictionary changed size during iteration
+
+Overridden parameters
+
+    >>> f(x=5, **{'x': 3}, y=2)
+    Traceback (most recent call last):
+      ...
+    TypeError: f() got multiple values for keyword argument 'x'
+
+    >>> f(**{'x': 3}, x=5, y=2)
+    Traceback (most recent call last):
+      ...
+    TypeError: f() got multiple values for keyword argument 'x'
+
+    >>> f(**{'x': 3}, **{'x': 5}, y=2)
+    Traceback (most recent call last):
+      ...
+    TypeError: f() got multiple values for keyword argument 'x'
+
+    >>> f(**{1: 3}, **{1: 5})
+    Traceback (most recent call last):
+      ...
+    TypeError: f() keywords must be strings
+
 Unpacking non-sequence
 
     >>> a, *b = 7
@@ -138,17 +315,17 @@ Now some general starred expressions (all fail).
     >>> *a # doctest:+ELLIPSIS
     Traceback (most recent call last):
       ...
-    SyntaxError: can use starred expression only as assignment target
+    SyntaxError: can't use starred expression here
 
     >>> *1 # doctest:+ELLIPSIS
     Traceback (most recent call last):
       ...
-    SyntaxError: can use starred expression only as assignment target
+    SyntaxError: can't use starred expression here
 
     >>> x = *a # doctest:+ELLIPSIS
     Traceback (most recent call last):
       ...
-    SyntaxError: can use starred expression only as assignment target
+    SyntaxError: can't use starred expression here
 
 Some size constraints (all fail.)