Nested list comprehension
When dealing with 2D lists, it’s also possible to iterate over objects with a list comprehension.
grid = [
[10, 20, 30],
[40, 50, 60],
]
squared = [[i * i for i in row] for row in grid]
print(squared)
# [[100, 400, 900], [1600, 2500, 3600]]Here the outer loop goes over the
grid row-by-row. Then we iterate over each item in a row.In case we don’t want to have a 2D list as a result, we can flatten out the grid by omitting the inner brackets and moving the
for i in row out of the inner loop. We first iterate over the grid with for row in grid and then for i in row:grid = [
[10, 20, 30],
[40, 50, 60],
]
squared = [i * i for row in grid for i in row]
print(squared)
# [100, 400, 900, 1600, 2500, 3600]Challenge
Can you use list comprehension to print out all the coordinates of a chessboard?
The numbers go from 1 to 8, and the letters are
A B C D E F G H. The numbering goes like A1 B1 C1 ... H1 the next line is A2 B2 C2 ... H2, etc. Print each line separately.Output
A1 B1 C1 D1 E1 F1 G1 H1
A2 B2 C2 D2 E2 F2 G2 H2
A3 B3 C3 D3 E3 F3 G3 H3
A4 B4 C4 D4 E4 F4 G4 H4
A5 B5 C5 D5 E5 F5 G5 H5
A6 B6 C6 D6 E6 F6 G6 H6
A7 B7 C7 D7 E7 F7 G7 H7
A8 B8 C8 D8 E8 F8 G8 H8Tip
You can use a single-line condition to determine if you’re printing a newline as the
end parameter of a print methodConstraints
Time limit: 2 seconds
Memory limit: 512 MB
Output limit: 1 MB