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?

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

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

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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!

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