Adding data to a nested list in Python

I have a nested list e.g.:

nlist = [
         [1, 2, 3], 
         [4, 5, 6], 
         [7, 8, 9],
        ]

Before I insert this list into a database, I would like to add a "column" to it with the same value in each row of the new column e.g:

nlist = [
            [a, 1, 2, 3], 
            [a, 4, 5, 6], 
   开发者_如何学Go         [a, 7, 8, 9],
           ]

What's the best way to do this, when, for example, the original nested list might have hundreds of rows?

Why not change the original list (if that is all you want to do):

for row in nlist:
    row.insert(0, a)

If you are looking to create a new list then this will work as well...

nlistnew = [[a]+row for row in nlist]

EDIT: Fixed code as per Felix Kling's comment. Thanks!

Iterate over your outer list. For each inner list use list method insert(0, new_data).