Gabriel Genellina wrote: > En Fri, 20 Apr 2007 14:28:00 -0300, Larry Bates > <[EMAIL PROTECTED]> escribió: > >> Bill Jackson wrote: >>> What is the benefit of clearing a dictionary, when you can just reassign >>> it as empty? >> >> If you have objects that point to the dictionary (something like a cache) >> then you want to clear the existing dictionary instead of just assigning >> it to empty. If nothing points to it, assigning it to empty is fast and >> you can let garbage collection do the rest. > > For an actual comparision, see Alex Martelli posts a few days ago: > http://mail.python.org/pipermail/python-list/2007-March/433027.html > >>>>>> a = {1:2,3:4} >>>>>> b = {1:2:4:3} >>>>>> a.clear() >>>>>> a.update(b) >>> >>>>>> a = {1:2,3:4} >>>>>> b = {1:2,4:3} >>>>>> for key in b: >>> ... a[key] = b[key] >>> > >> Syntax error in the first example but if you fix that the first two are >> equivalent (but I would suspect that the second would be faster for large >> dictionaries). > > It's the other way; the first method contains a single Python function > call and most of the work is done in C code; the second does the > iteration in Python code and is about 4x slower. > >> python -m timeit -s "b=dict.fromkeys(range(10000));a={}" "a.update(b)" > 100 loops, best of 3: 10.2 msec per loop > >> python -m timeit -s "b=dict.fromkeys(range(10000));a={}" "for key in >> b: a[key]=b[key]" > 10 loops, best of 3: 39.6 msec per loop > > --Gabriel Genellina
That is what I meant to say, thanks for catching the error. -Larry -- http://mail.python.org/mailman/listinfo/python-list
