Write a program that creates and stores a scalable Z, then prints it. 

Do this twice: 

1. Using a list of lists for storage in your implementation.

2. Using a dictionary for storage in your implementation. 

Here's the starting point: 

size = int(raw_input("Size: "))

for line in range(size):
    for column in range(size):
        if line == 0 or line == size-1 or line+column == size-1 or \
           line == size/2 and size/4 < column < 3 * size/4:
            print "*",
        else:
            print " ",
    print

We then wrote these: 

def show(matrix):
    for line in range(len(matrix)):
        for column in range(len(matrix[line])):
            print matrix[line][column],
        print

def generate(columns, lines):
    matrix = []
    for line in range(lines):
        row = []
        for column in range(columns):
            row.append(' ')
        matrix.append(row)
    return matrix

def setZ(matrix):
    size = len(matrix)
    for line in range(size):
        for column in range(size):
            if line == 0 or line == size-1 or line+column == size-1 or \
               line == size/2 and size/4 < column < 3 * size/4:
                matrix[line][column] = "*"
            else:
                matrix[line][column] = " "

size = int(raw_input("Size: "))
board = generate(size, size)
setZ(board)
show(board)

We then changed the representation and the new code became: 


def show(matrix):
    for line in range(matrix["height"]):
        for column in range(matrix["width"]):
            print matrix[line, column],
        print

def generate(columns, lines):
    matrix = {}
    matrix["height"] = lines
    matrix["width"] = columns    
    for line in range(lines):
        for column in range(columns):
            matrix[line, column] = '*'
    return matrix

def setZ(matrix):
    size = matrix["width"]
    for line in range(size):
        for column in range(size):
            if line == 0 or line == size-1 or line+column == size-1 or \
               line == size/2 and size/4 < column < 3 * size/4:
                matrix[line, column] = "*"
            else:
                matrix[line, column] = " "

size = int(raw_input("Size: "))
board = generate(size, size)
setZ(board)
show(board)


Notice that the "main program" that is, the last four lines, are representation independent.

That is, the generate, show and setZ functions hide the internal representation from their users.