[EMAIL PROTECTED] wrote: > Hi folks, > > Thanks, for all the help. I tried running the various options, and > here is what I found: > > > from array import array > from time import time > > def f1(recs, cols): > for r in recs: > for i,v in enumerate(r): > cols[i].append(v) > > def f2(recs, cols): > for r in recs: > for v,c in zip(r, cols): > c.append(v) > > def f3(recs, cols): > for r in recs: > map(list.append, cols, r) > > def f4(recs): > return zip(*recs) > > records = [ tuple(range(10)) for i in xrange(1000000) ] > > columns = tuple([] for i in xrange(10)) > t = time() > f1(records, columns) > print 'f1: ', time()-t > > columns = tuple([] for i in xrange(10)) > t = time() > f2(records, columns) > print 'f2: ', time()-t > > columns = tuple([] for i in xrange(10)) > t = time() > f3(records, columns) > print 'f3: ', time()-t > > t = time() > columns = f4(records) > print 'f4: ', time()-t > > f1: 5.10132408142 > f2: 5.06787180901 > f3: 4.04700708389 > f4: 19.13633203506 > > So there is some benefit in using map(list.append). f4 is very clever > and cool but it doesn't seem to scale. > > Incidentally, it took me a while to figure out why the following > initialization doesn't work: > columns = ([],)*10 > apparently you end up with 10 copies of the same list. >
Yes. A well known gotcha in Python and a FAQ. > Finally, in my case the output columns are integer arrays (to save > memory). I can still use array.append but it's a little slower so the > difference between f1-f3 gets even smaller. f4 is not an option with > arrays. > -- http://mail.python.org/mailman/listinfo/python-list
