New submission from Xavier Morel <bugs.pypy.org@masklinn.net>: In CPython, as the number of keys grow dict.update settles at roughly half the speed of an equivalent bunch of dict[key]=value sequence: > python2.7 -m timeit -s 'd = {}' 'd["foo"] = 3' 'd["bar"] = 4' 'd["baz"] = 5' 'd["qux"] = 6' 'd["quux"] = 7' 1000000 loops, best of 3: 0.395 usec per loop > python2.7 -m timeit -s 'd = {}' 'd.update(foo=3, bar=4, baz=5, qux=6, quux=7)' 1000000 loops, best of 3: 0.657 usec per loop In Pypy, on the other hand, the difference in speed is on the order of 20x, even while setting 5 keys and dict.update is ~30% the speed of the equivalent call in CPython at almost 2µsec/loop to CPython's 0.66µsec/loop, while pypy's __setitem__ is more than 4 times faster than CPython: > pypy-c -m timeit -s 'd = {}' 'd["foo"] = 3' 'd["bar"] = 4' 'd["baz"] = 5' 'd["qux"] = 6' 'd["quux"] = 7' 10000000 loops, best of 3: 0.0877 usec per loop > pypy-c -m timeit -s 'd = {}' 'd.update(foo=3, bar=4, baz=5, qux=6, quux=7)' 100000 loops, best of 3: 1.95 usec per loop that kind-of bothers me, as I tend to use dict.update over long sequences of setitem for readability purpose. Now of course half a µsec per call is not a big difference in absolute, but still… Versions information: * OSX 10.6.8 * CPython 2.7.2 (Macports) * Pypy 1.7.0 Python 2.7.1 (?, Nov 24 2011, 10:57:50) (Macports) ---------- messages: 3814 nosy: masklinn, pypy-issue priority: performance bug status: unread title: dict.update significantly slower than series of dict.__setitem__ ________________________________________ PyPy bug tracker <tracker@bugs.pypy.org> <https://bugs.pypy.org/issue1022> ________________________________________