Python - Inserting a column to an existing list of lists (fixed value or numerical count/index)

# 1. Original matrixmatrix = [
        [1, 'a', 'the letter a']
        , [2, 'b', 'the letter b']
    ]

# 2. Inserting the same fixed valuematrix = [
        x + ['new fixed value']
        for x in matrix
    ]

# 3. Insert a consecutive numeric valuematrix = [
        pair[1] + [pair[0]]
        for pair
        in enumerate(matrix)
    ]