code: def int_to_key(value, base=BASE62):
      
      def key_sequence_generator(value, base):
          """
          Generator for producing sequence of characters of a key providing an
          integer value and a base of characters for encoding, such as Base62
          for instance.
  
          @param value: a positive integer.
          @param base: a sequence of characters that is used to encode the
                 integer value.
  
          @return: the next character of the object's key encoded with the
                   specified base.
              """
          base_length = len(base)
          while True:
              yield base[value % base_length]
              if value < base_length:
                  break
              value /= base_length
  
      return ''.join([ c for c in key_sequence_generator(value, base) ])
docs: Convert the specified integer to a key using the given base.
  
      @param value: a positive integer.
  
      @param base: a sequence of characters that is used to encode the
             integer value.
  
      @return: a key expressed in the specified base.