Generator that yields 2D list values.

diag.py

"""
Diagonal array generator.  
Start at top right corner going diagonally up
and end in the bottom left corner.
Bruce Wernick
13 August 2025
"""

def diag(arr):
  nr = len(arr)
  nc = len(arr[0])
  for k in range(nr+nc-1):
    for c in range(nc-1,-1,-1):
      for r in range(nr-1,-1,-1):
        if (r - c) + nc - 1 == k:
          yield(arr[r][c])


# Usage:

arr = [[1,2,3],
       [4,5,6],
       [7,8,9]]
# expect: 3,6,2,9,5,1,8,4,7
for a in diag(arr):
  print(a, end=",")
print("\n")

arr = [[ 1, 2, 3, 4],
       [ 5, 6, 7, 8],
       [ 9,10,11,12],
       [13,14,15,16],
       [17,18,19,20],
       [21,22,23,24],
       [25,26,27,28]]
for a in diag(arr):
  print(a, end=",")
print("\n")

arr = [[ 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12],
       [13,14,15,16,17,18,19,20,21,22,23,24],
       [25,26,27,28,29,30,31,32,33,34,35,36]]
for a in diag(arr):
  print(a, end=",")
print("\n")


# Use a list comprehension to create a list of any size
rows, cols = 14, 4
arr = [[1+c+r*cols for c in range(cols)] for r in range(rows)]
for a in diag(arr):
  print(a, end=",")
print("\n")