can we append a list with another list in Python ?

[inshu chauhan]

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.ws at gmail.com>wrote:

> On 23/10/2012, inshu chauhan <insideshoes at 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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