PEP-0318, @decorator-style. In Guido's words:

"@ seems the syntax that everybody can hate equally"
Implementation by Mark Russell, from SF #979728.

Lib/test/test_decorators.py

@@ -0,0 +1,194 @@
+import unittest
+from test import test_support
+
+def funcattrs(**kwds):
+    def decorate(func):
+        func.__dict__.update(kwds)
+        return func
+    return decorate
+
+class MiscDecorators (object):
+    @staticmethod
+    def author(name):
+        def decorate(func):
+            func.__dict__['author'] = name
+            return func
+        return decorate
+
+# -----------------------------------------------
+
+class DbcheckError (Exception):
+    def __init__(self, exprstr, func, args, kwds):
+        # A real version of this would set attributes here
+        Exception.__init__(self, "dbcheck %r failed (func=%s args=%s kwds=%s)" %
+                           (exprstr, func, args, kwds))
+    
+    
+def dbcheck(exprstr, globals=None, locals=None):
+    "Decorator to implement debugging assertions"
+    def decorate(func):
+        expr = compile(exprstr, "dbcheck-%s" % func.func_name, "eval")
+        def check(*args, **kwds):
+            if not eval(expr, globals, locals):
+                raise DbcheckError(exprstr, func, args, kwds)
+            return func(*args, **kwds)
+        return check
+    return decorate
+
+# -----------------------------------------------
+
+def countcalls(counts):
+    "Decorator to count calls to a function"
+    def decorate(func):
+        name = func.func_name
+        counts[name] = 0
+        def call(*args, **kwds):
+            counts[name] += 1
+            return func(*args, **kwds)
+        # XXX: Would like to say: call.func_name = func.func_name here
+        #      to make nested decorators work in any order, but func_name
+        #      is a readonly attribute
+        return call
+    return decorate
+
+# -----------------------------------------------
+
+def memoize(func):
+    saved = {}
+    def call(*args):
+        try:
+            return saved[args]
+        except KeyError:
+            res = func(*args)
+            saved[args] = res
+            return res
+        except TypeError:
+            # Unhashable argument
+            return func(*args)
+    return call
+            
+# -----------------------------------------------
+
+class TestDecorators(unittest.TestCase):
+
+    def test_single(self):
+        class C(object):
+            @staticmethod
+            def foo(): return 42
+        self.assertEqual(C.foo(), 42)
+        self.assertEqual(C().foo(), 42)
+
+    def test_dotted(self):
+        decorators = MiscDecorators()
+        @decorators.author('Cleese')
+        def foo(): return 42
+        self.assertEqual(foo(), 42)
+        self.assertEqual(foo.author, 'Cleese')
+
+    def test_argforms(self):
+        # A few tests of argument passing, as we use restricted form
+        # of expressions for decorators.
+        
+        def noteargs(*args, **kwds):
+            def decorate(func):
+                setattr(func, 'dbval', (args, kwds))
+                return func
+            return decorate
+
+        args = ( 'Now', 'is', 'the', 'time' )
+        kwds = dict(one=1, two=2)
+        @noteargs(*args, **kwds)
+        def f1(): return 42
+        self.assertEqual(f1(), 42)
+        self.assertEqual(f1.dbval, (args, kwds))
+
+        @noteargs('terry', 'gilliam', eric='idle', john='cleese')
+        def f2(): return 84
+        self.assertEqual(f2(), 84)
+        self.assertEqual(f2.dbval, (('terry', 'gilliam'),
+                                     dict(eric='idle', john='cleese')))
+
+        @noteargs(1, 2,)
+        def f3(): pass
+        self.assertEqual(f3.dbval, ((1, 2), {}))
+
+    def test_dbcheck(self):
+        @dbcheck('args[1] is not None')
+        def f(a, b):
+            return a + b
+        self.assertEqual(f(1, 2), 3)
+        self.assertRaises(DbcheckError, f, 1, None)
+
+    def test_memoize(self):
+        # XXX: This doesn't work unless memoize is the last decorator -
+        #      see the comment in countcalls.
+        counts = {}
+        @countcalls(counts) @memoize 
+        def double(x):
+            return x * 2
+
+        self.assertEqual(counts, dict(double=0))
+
+        # Only the first call with a given argument bumps the call count:
+        #
+        self.assertEqual(double(2), 4)
+        self.assertEqual(counts['double'], 1)
+        self.assertEqual(double(2), 4)
+        self.assertEqual(counts['double'], 1)
+        self.assertEqual(double(3), 6)
+        self.assertEqual(counts['double'], 2)
+
+        # Unhashable arguments do not get memoized:
+        #
+        self.assertEqual(double([10]), [10, 10])
+        self.assertEqual(counts['double'], 3)
+        self.assertEqual(double([10]), [10, 10])
+        self.assertEqual(counts['double'], 4)
+
+    def test_errors(self):
+        # Test syntax restrictions - these are all compile-time errors:
+        #
+        for expr in [ "1+2", "x[3]", "(1, 2)" ]:
+            # Sanity check: is expr is a valid expression by itself?
+            compile(expr, "testexpr", "exec")
+            
+            codestr = "@%s\ndef f(): pass" % expr
+            self.assertRaises(SyntaxError, compile, codestr, "test", "exec")
+
+        # Test runtime errors
+
+        def unimp(func):
+            raise NotImplementedError
+        context = dict(nullval=None, unimp=unimp)
+        
+        for expr, exc in [ ("undef", NameError),
+                           ("nullval", TypeError),
+                           ("nullval.attr", AttributeError),
+                           ("unimp", NotImplementedError)]:
+            codestr = "@%s\ndef f(): pass\nassert f() is None" % expr
+            code = compile(codestr, "test", "exec")
+            self.assertRaises(exc, eval, code, context)
+
+    def test_double(self):
+        class C(object):
+            @funcattrs(abc=1, xyz="haha")
+            @funcattrs(booh=42)
+            def foo(self): return 42
+        self.assertEqual(C().foo(), 42)
+        self.assertEqual(C.foo.abc, 1)
+        self.assertEqual(C.foo.xyz, "haha")
+        self.assertEqual(C.foo.booh, 42)
+
+    def test_order(self):
+        class C(object):
+            @funcattrs(abc=1) @staticmethod
+            def foo(): return 42
+        # This wouldn't work if staticmethod was called first
+        self.assertEqual(C.foo(), 42)
+        self.assertEqual(C().foo(), 42)
+
+def test_main():
+    test_support.run_unittest(TestDecorators)
+
+if __name__=="__main__":
+    test_main()