Nick Craig-Wood wrote: > The optimized += depends on their being no other references to the > string. Strings are immutable in python. So append must return a new > string. However the += operation was optimised to do an in-place > append if and only if there are no other references to the string. > > You can see this demonstrated here > > $ python -m timeit -s 'a="x"' 'a+="x"' > 1000000 loops, best of 3: 0.231 usec per loop > > $ python -m timeit -s 'a="x"; b=a' 's = a; a+="x"' > 100000 loops, best of 3: 30.1 usec per loop
That is a fantastic explanation of why you shouldn't rely on the concat optimization, although the assignment b=a in the setup isn't necessary and is a little misleading. Thank you. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
