how list comprehension for 2D works

[[float(c) for c in row] for row in data]

dx = [3, 4, 5, 9]
dy = [5, 3, 2, 1]
output_matrix = []
 
for dx_n in dx:
	dx_row = []
	for dy_n in dy:
		dx_row.append(dx_n * dy_n)
	output_matrix.append(dx_row)
 
# Output is [[15, 9, 6, 3], [20, 12, 8, 4], [25, 15, 10, 5], [45, 27, 18, 9]]