def __init__(self, handler_spec, input_reader_spec, params, shard_count):
    """Creates a new MapperSpec.

    Args:
      handler_spec: handler specification as string (see class doc for
        details).
      input_reader_spec: The class name of the input reader to use.
      params: Dictionary of additional parameters for the mapper.
      shard_count: number of shards to process in parallel.

    Properties:
      handler_spec: name of handler class/function to use.
      shard_count: number of shards to process in parallel.
      handler: cached instance of mapper handler as callable.
      input_reader_spec: The class name of the input reader to use.
      params: Dictionary of additional parameters for the mapper.
    """
    self.handler_spec = handler_spec
    self.__handler = None
    self.input_reader_spec = input_reader_spec
    self.shard_count = shard_count
    self.params = params
Creates a new MapperSpec.

    Args:
      handler_spec: handler specification as string (see class doc for
        details).
      input_reader_spec: The class name of the input reader to use.
      params: Dictionary of additional parameters for the mapper.
      shard_count: number of shards to process in parallel.

    Properties:
      handler_spec: name of handler class/function to use.
      shard_count: number of shards to process in parallel.
      handler: cached instance of mapper handler as callable.
      input_reader_spec: The class name of the input reader to use.
      params: Dictionary of additional parameters for the mapper.
    
mapreduce/model.py