In-Order Walk

def nextCell(s):
  l = len(s)
  row = ord(s[l-1:l])-ord('A')
  col = int(s[0:l-1])+1
  if (col > 12):
    col = 1
    row += 1
    if (row > 7):
      row = 0
  row = chr(row + ord('A'))
  return "{0}{1}".format(col,row)

print("3C => ", nextCell("3C"))
print("12C => ", nextCell("12C"))
print("12H => ", nextCell("12H"))