2009/7/17 Dinesh B Vadhia <dineshbvad...@hotmail.com>: > This was discussed in a previous post but I didn't see a solution. Say, you > have > > for i in veryLongListOfStringValues: > s += i > > As per previous post > (http://thread.gmane.org/gmane.comp.python.tutor/54029/focus=54139), > (quoting verbatim) "... the following happens inside the python interpreter: > > 1. get a reference to the current value of s. > 2. get a reference to the string value i. > 3. compute the new value += i, store it in memory, and make a reference to > it. > 4. drop the old reference of s (thus free-ing "abc") > 5. give s a reference to the newly computed value. > > After step 3 and before step 4, the old value of s is still referenced by s, > and the new value is referenced internally (so step 5 can be performed). In > other words, both the old and the new value are in memory at the same time > after step 3 and before step 4, and both are referenced (that is, they > cannot be garbage collected). ... " > > As s gets very large, how do you deal with this situation to avoid a memory > error or what I think will be a general slowing down of the system if the > for-loop is repeated a large number of times. > > Dinesh > > _______________________________________________ > Tutor maillist - tu...@python.org > http://mail.python.org/mailman/listinfo/tutor > >
If all you are doing is concatenating a list of strings, use the str.join() method, which is designed for the job: >>> listOfStrings ['And', 'now', 'for', 'something', 'completely', 'different.'] >>> print " ".join(listOfStrings) And now for something completely different. >>> print "_".join(listOfStrings) And_now_for_something_completely_different. If you need to perform other operations first, you can pass a generator expression as the argument, for example: >>> " ".join((s.upper() if n%2 else s.lower()) for n, s in >>> enumerate(listOfStrings)) 'and NOW for SOMETHING completely DIFFERENT.' Hope that helps you. -- Rich "Roadie Rich" Lovely There are 10 types of people in the world: those who know binary, those who do not, and those who are off by one. _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
