Use set/dict literal syntax (#169)

* Use set/dict literal syntax

Every supported version can use this syntax, and it's both faster and clearer.

* Fix indentation and drop unused argument

The `op` arg isn't used for creating `out_names`, so we elide it.

cloudpickle/cloudpickle.py

@@ -578,8 +578,7 @@ def extract_code_globals(cls, co):
                 # PyPy "builtin-code" object
                 out_names = set()
             else:
-                out_names = set(names[oparg]
-                                for op, oparg in _walk_global_ops(co))
+                out_names = {names[oparg] for _, oparg in _walk_global_ops(co)}
 
                 # see if nested function have any global refs
                 if co.co_consts:

tests/cloudpickle_test.py

@@ -222,7 +222,7 @@ def g():
 
     def test_unhashable_closure(self):
         def f():
-            s = set((1, 2))  # mutable set is unhashable
+            s = {1, 2}  # mutable set is unhashable
 
             def g():
                 return len(s)
@@ -494,7 +494,7 @@ def test_extended_arg(self):
         nvars = 65537 + 258
         names = ['g%d' % i for i in range(1, nvars)]
         r = random.Random(42)
-        d = dict([(name, r.randrange(100)) for name in names])
+        d = {name: r.randrange(100) for name in names}
         # def f(x):
         #     x = g1, g2, ...
         #     return zlib.crc32(bytes(bytearray(x)))
@@ -693,7 +693,7 @@ def __init__(self, x):
         self.assertEqual(depickled3.x, 3)
         self.assertEqual(len(weakset), 2)
 
-        self.assertEqual(set(weakset), set([depickled1, depickled2]))
+        self.assertEqual(set(weakset), {depickled1, depickled2})
 
     def test_faulty_module(self):
         for module_name in ['_faulty_module', '_missing_module', None]: