def minesweeper(field):
  """Takes a single string with newlines, consisting of '*' (mines) and other
  characters (non-mines), and returns a string with numbers corresponding to the
  number of mines around each cell.

  >>> print(minesweeper("...*.\n....."))
  001*1
  00111

  Hint for the algorithm: a cell is either a mine or a count of mines around it.
  """

  lines = field.splitlines()
  rows = len(lines)
  cols = len(lines[0]) if rows > 0 else 0

  def isMine((r,c)):
    return lines[r][c] == '*'

  def neighbours((r,c)):
    return [(rr,cc) for rr in range(max(0,r-1), min(r+2, rows))  # r+2 here since
                    for cc in range(max(0,c-1), min(c+2, cols))] # range() is not inclusive

  def count(cell):
    return '*' if isMine(cell) else str(
        sum([1 if isMine(neighbour) else 0 for neighbour in neighbours(cell)]))

  def join(strings):
    return reduce(lambda x, y: x+y, strings)

  def toField(nums):
    return '' if len(nums) == 0 else join(nums[0:cols]) + '\n' + toField(nums[cols:])


  cells = [(r,c) for r in range(rows) for c in range(cols)]

  return toField(map(count, cells))