Nested List Question

[Newsfeeds]

Hello All,

  Could anyone tell me why this code produces the output it does?

noAdjacencies = 2
gridsPerAdj = 3
rows = 4
columns = 5


gridSystemId = [[None]*columns]*rows
for row in range(rows):
    for column in range(columns):
        gridSystemId[row][column] = "%d-%d" % (row,column)

print gridSystemId

Produces:

[['3-0', '3-1', '3-2', '3-3', '3-4'], ['3-0', '3-1', '3-2', '3-3', '3-4'], 
['3-0
', '3-1', '3-2', '3-3', '3-4'], ['3-0', '3-1', '3-2', '3-3', '3-4']]

Rather than:

[['0-0', '0-1', '0-2', '0-3', '0-4'], ['1-0', '1-1', '1-2', '1-3', '1-4'], 
['2-0
', '2-1', '2-2', '2-3', '2-4'], ['3-0', '3-1', '3-2', '3-3', '3-4']]

Thanks for your help,
Chris M. 



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