docs: def int2base36(n):
      """
      Convert int base10 to base36.
      Back convert: int('<base36>', 36)
      """
      assert isinstance(n, (int, long))
      c = '0123456789abcdefghijklmnopqrstuvwxyz'
      if n < 0:
          return '-' + int2base36(-n)
      elif n < 36:
          return c[n]
      b36 = ''
      while n != 0:
          n, i = divmod(n, 36)
          b36 = c[i] + b36
      return b36