Inserting values in 2D lists in Python

Question

I'm looking for a method of inserting values to 2D lists in Python. My sample list is as follows:

List= [ ['A', 'B'], ['C', 'D'] ]

I would like to insert a value at the beginning of each list within my List, so that it would look like this:

List = [ ['#','A', 'B'], ['#','C', 'D'] ]

I have written a function as follows:

def Foo(l):
    rows = len(l)
    cols = len(l[0])
    for row in xrange(rows):
        l.insert(row, '#')

But that has given me the following output:

List= [ '#', '#', ['A', 'B'], ['C', 'D'] ]

Tadhg McDonald-Jensen · Accepted Answer · 2016-04-04 03:04:16Z

5

when you do l.insert() it adds an item to l not the sub lists, to iterate over the sub lists you can do:

for row in l:
    row.insert(0,"#")

Or using xrange:

for i in xrange(len(l)):
    l[i].insert(0,"#")

answered Apr 4, 2016 at 3:04

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