grid = []			# grid will be a list of lists, i.e. list of rows

""" if we create one row outside the loop and append it 3 times
then setting [0][2] will actually set [n][2] which is column 2 in every row
duplicate references """

for y in range(3):		# create 3 rows
	row = [0] *4		# create a new row each time with 4 columns
	grid.append(row)	# method to add an element to the list

print grid
print "------------\n"

grid[0][2] = 5			# row 0, column 2; index order from right to left

# print grid

for y in grid:			# y is a list
	# t = type(y)
	# print t
	print y
print "------------\n"



# list comprehension, can run twice as fast
# somewhat inverted syntax in that expression precedes iterator

d = [ [9]*4 for y in range(3) ]
print d
print "------------\n"

d[0][3] = 1

for row in d:
	print row
print "------------\n"


# 3-D array:  2 planes with 3 rows of 4 columns

# only do one [n]*m otherwise it will duplicate references to a list
d = [ [[9]*4 for y in range(3)] for z in range(2) ]
print d
print "------------\n"

d[0][2][1] = 1		# plane 0, row 2, column 1

print d
print "------------\n"

for plane in d:
	for row in plane:
		print row
	print "------------"