'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.'

def __init__(self, handler_spec, input_reader_spec, params, shard_count):

    self.handler_spec = handler_spec
    self.__handler = None
    self.input_reader_spec = input_reader_spec
    self.shard_count = shard_count
    self.params = params
