My solution for sudoku checker in online course Software testing

sudoku_checker.py

def check_sudoku(grid):
  ###Your code here.
  if isIllFormed(grid):
    return None
  elif isInvalid(grid):
    return False
  else:
    return True

# return True if the grid is ill_formed
# 1. has a list with !9 size
# 2. has an elment more than 9 or less than 0
# return True if invalid, False otherwise
def isIllFormed(g):
  for li in g:
    if len(li) != 9:
      return True
    else:
      for i in li:
        if i > 9 or i < 0:
          return True
  else:
      return False


# check if the whole grid is invalid
# return True if invalid, False otherwise
def isInvalid(grid):
  inval = False
  columns = [[] for i in range(len(grid))]
  boxes = [[] for i in range(len(grid))]
  # check invalid for all rows
  # generate lists for columns and boxes
  for li in grid:
    if inval == False:
      inval = checkInvalid(li)
    # collect each column of the grid into columns list
    map(lambda x, y: y.append(x), li, columns)
    # collect each box of the grid into boxes list
    row = grid.index(li)
    col = 0
    for i in li:
      boxes[boxNumber(row, col)].append(i)
      col += 1
  # check invalid for all boxes
  for box in boxes:
    if inval == False:
      inval = checkInvalid(box)

  # check invalid for all columns
  for li in columns:
    if inval == False:
      inval = checkInvalid(li)
  return inval

def boxNumber(row, col):
  return col/3 + (row/3)*3

# check if a single column/row/box is invalid
# return True if invalid, False otherwise
def checkInvalid(li):
  count = [0 for i in range(10)]
  for i in range(len(li)):
    count[li[i]] += 1
  if max(count[1:]) > 1:
    return True
  else:
    return False