On Sat, Nov 12, 2011 at 9:22 PM, Dave Angel <d...@davea.name> wrote: > On 11/12/2011 03:54 AM, lina wrote: >> >> <SNIP> >> The one I tried : >> if longest>= 2: >> sublist=L1[x_longest-longest:x_longest] >> result=result.append(sublist) >> if sublist not in sublists: >> sublists.append(sublist) >> >> the $ python3 CommonSublists.py >> atom-pair_1.txt atom-pair_2.txt >> Traceback (most recent call last): >> File "CommonSublists.py", line 47, in<module> >> print(CommonSublist(a,b)) >> File "CommonSublists.py", line 24, in CommonSublist >> result=result.append(sublist) >> AttributeError: 'NoneType' object has no attribute 'append' >> >> in local domain I set the result=[] >> I don't know why it complains its NoneType, since the "result" is >> nearly the same as "sublists". >> > Assuming this snippet is part of a loop, I see the problem: > > result = result.append(sublist) > > list.append() returns none. It modifies the list object in place, but it > doesn't return anything. So that statement modifies the result object, > appending the sublist to it, then it sets it to None. The second time > around you see that error.
I am sorry. haha ... still lack of understanding above sentence. >>> a ['3', '5', '7', '8', '9'] >>> d.append(a) >>> d [['3', '5', '7', '8', '9']] >>> type(a) <class 'list'> Sorry and thanks, best regards, lina > > In general, most methods in the standard library either modify the object > they're working on, OR they return something. The append method is in the > first category. > > > -- > > DaveA > > _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
