nested for loop in comprehension code example

Example: nested loop in list comprehension

# 2-D List 
matrix = [[1, 2, 3], [4, 5], [6, 7, 8, 9]] 
  
# Nested List Comprehension to flatten a given 2-D matrix 
flatten_matrix = [val for sublist in matrix for val in sublist] 
  
print(flatten_matrix)