Insert at first position of a list in Python

Question

How can I insert an element at the first index of a list? If I use list.insert(0, elem), does elem modify the content of the first index? Or do I have to create a new list with the first elem and then copy the old list inside this new one?

Solution 1

Use insert:

In [1]: ls = [1,2,3]

In [2]: ls.insert(0, "new")

In [3]: ls
Out[3]: ['new', 1, 2, 3]

Solution 2

From the documentation:

list.insert(i, x)
Insert an item at a given position. The first argument is the index of the element before which to insert, so a.insert(0, x) inserts at the front of the list, and a.insert(len(a),x) is equivalent to a.append(x)

http://docs.python.org/2/tutorial/datastructures.html#more-on-lists

Comments

[Gino Mempin]

It's a duplicate of What's the idiomatic syntax for prepending to a short python list?.