Thankyou.. but my problem is different than simply joining 2 lists and it is done now :)....
On Tue, Oct 23, 2012 at 11:38 AM, Joshua Landau <joshua.landau...@gmail.com>wrote: > On 23/10/2012, inshu chauhan <insidesh...@gmail.com> wrote: > > can we append a list with another list in Python ? using the normal > routine > > syntax but with a for loop ?? > > I assume you want to join two lists. > > You are corrrect that we can do: > > >>> start = [1, 2, 3, 4] > >>> end = [5, 6, 7, 8] > >>> > >>> for end_item in end: > >>> start.append(end_item) > >>> > >>> print(start) > [1, 2, 3, 4, 5, 6, 7, 8] > >>> > > However, it is markedly repetitive, no? > This is a common enough operation that there is a shortcut to find out > about it. > > If you want to find out what methods there are, try "help(...)". I > can't stress this enough. > > >>> help(start) > Help on list object: > > class list(object) > | list() -> new empty list > | list(iterable) -> new list initialized from iterable's items > | > | Methods defined here: > | > | __add__(...) > | x.__add__(y) <==> x+y > ... > | append(...) > | L.append(object) -- append object to end > ... > | extend(...) > | L.extend(iterable) -- extend list by appending elements from > the iterable > ... > > So list.extend seems to do exactly this! > > You can always check the documentation > <http://docs.python.org/tutorial/datastructures.html>. > An lo! The documentation says "start.extend(end)" is _equivilant_ to > "start[len(start):] = end". > > Why? > > Well, this uses the slicing syntax. > > >>> start[:3] > [1, 2, 3] > >>> start[3:] > [4] > >>> start[2:3] > [3] > > Wonderously, all these really say are "ranges" in the list. Hence, you > can "put" lists in their place. > > "start[len(start):] = end" means "start[-1:] = end", so what you're > doing is saying "the empty end part of the list is actually this new > list". Hopefully that makes sense. > > Finally, there is another method. Instead of *changing* the list, you > can make a new list which is equal to the others "added" together. > > >>> new = start + end > > _______________________________________________ > > Theses methods all have their own upsides. If you want to change the > list, use .extend(). If you want to change the list, but by putting > the new list somewhere inside the "old" one, use slicing: > > >>> start = [1, 2, 3, 4] > >>> end = [5, 6, 7, 8] > >>> > >>> start[2:2] = end > >>> print(start) > [1, 2, 5, 6, 7, 8, 3, 4] > > Looping is good for when you want to generate the extra items as you go > along. > > Finally, if you want to keep the old list or use these "inline", use "+". > > _______________________________________________ > > Note that, being in the unfortunate position of "away from an > interpreter", none of my examples are copy-pastes. Hence they may be > wrong :/ > > # Not checked for errors, typos and my "friends" messing with it. >
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