I have a 3x2 list called x and a 1x2 list called y:
x=[[1,2],[3,4],[5,6]]
and
y=[10,20]
my question is how to concatenate y to the end of x to end up with a 4x2 list like:
x=[[1,2],[3,4],[5,6],[10,20]]
I've tried this:
xx=[x,y]
but it gives me this which is not a 4x2 list:
xx=[[[1,2],[3,4],[5,6]],[10,20]]
>>> x = [[1, 2], [3, 4], [5, 6]]
>>> x
[[1, 2], [3, 4], [5, 6]]
>>> x.append([10, 20])
>>> x
[[1, 2], [3, 4], [5, 6], [10, 20]]
Or:
>>> x = [[1, 2], [3, 4], [5, 6]]
>>> x
[[1, 2], [3, 4], [5, 6]]
>>> x += [[10, 20]] # a list with a list as its only element
>>> x
[[1, 2], [3, 4], [5, 6], [10, 20]]
Given:
x = [[1,2],[3,4],[5,6]]
y = [10,20]
this:
x.append(y)
will give you:
[[1, 2], [3, 4], [5, 6], [10, 20]]
Note however that this modifies x.
If you don't want to modify x, this is another way:
xx = x + [y[:]]
setting xx to:
[[1, 2], [3, 4], [5, 6], [10, 20]]
We use y[:] rather than simply y in the above assignment because we want to create separate copy of y for xx so later, should (the original) y be modified it would not lead to changes in xx.
xx by modifying y. (e.g. xx = x + [y]; y.append(3)).
[y[:]] instead of just [y]. That way, the OP (or anyone else who comes across this) can have all the information necessary to pick which form is more appropriate for their application. My guess is that creating a shallow copy is probably unnecessary here, but the question is a little too vague to really know for sure.>>> x=[[1,2],[3,4],[5,6]]
>>> y=[10,20]
>>> x.append(y) # or x.append(list(y)) to append a shallow copy of y
>>> x
[[1, 2], [3, 4], [5, 6], [10, 20]]
list(y) means that changes to y won't show up in x. In other words, list(y) appends a (shallow) copy of y instead of the actual object.
y can just go its merry way somewhere else. Ashwini has made a good comment and update here... so +1 from me for this one.If you want a new list:
z = x + [y]
Note, that using [y] makes the content a list within a list, so that this works.
If you want to modify x inplace, then:
x.append(y)
Although I don't use it often myself, I think it's worth mentioning the list's extend member function:
>>> x=[[1,2],[3,4],[5,6]]
>>> y=[10,20]
>>> x.extend([y])
>>> x
[[1, 2], [3, 4], [5, 6], [10, 20]]
http://docs.python.org/tutorial/datastructures.html#more-on-lists
