def start_map(name,
              handler_spec,
              reader_spec,
              reader_parameters,
              shard_count,
              mapreduce_parameters={},
              base_path="/mapreduce",
              queue_name="default",
              eta=None,
              countdown=None,
              _app=None):
  """Start a new, mapper-only mapreduce.

  Args:
    name: mapreduce name. Used only for display purposes.
    handler_spec: fully qualified name of mapper handler function/class to call.
    reader_spec: fully qualified name of mapper reader to use
    reader_parameters: dictionary of parameters to pass to reader. These are
      reader-specific.
    shard_count: number of shards to create.
    mapreduce_parameters: dictionary of mapreduce parameters relevant to the
      whole job.
    base_path: base path of mapreduce library handler specified in app.yaml.
      "/mapreduce" by default.
    queue_name: executor queue name to be used for mapreduce tasks.
    eta: Absolute time when the MR should execute. May not be specified
        if 'countdown' is also supplied. This may be timezone-aware or
        timezone-naive.
    countdown: Time in seconds into the future that this MR should execute.
        Defaults to zero.

  Returns:
    mapreduce id as string.
  """
  mapper_spec = model.MapperSpec(handler_spec, reader_spec, reader_parameters,
                                 shard_count)

  return handlers.StartJobHandler._start_map(
      name,
      mapper_spec,
      mapreduce_parameters,
      base_path=base_path,
      queue_name=queue_name,
      eta=eta,
      countdown=countdown,
      _app=_app)
Start a new, mapper-only mapreduce.

  Args:
    name: mapreduce name. Used only for display purposes.
    handler_spec: fully qualified name of mapper handler function/class to call.
    reader_spec: fully qualified name of mapper reader to use
    reader_parameters: dictionary of parameters to pass to reader. These are
      reader-specific.
    shard_count: number of shards to create.
    mapreduce_parameters: dictionary of mapreduce parameters relevant to the
      whole job.
    base_path: base path of mapreduce library handler specified in app.yaml.
      "/mapreduce" by default.
    queue_name: executor queue name to be used for mapreduce tasks.
    eta: Absolute time when the MR should execute. May not be specified
        if 'countdown' is also supplied. This may be timezone-aware or
        timezone-naive.
    countdown: Time in seconds into the future that this MR should execute.
        Defaults to zero.

  Returns:
    mapreduce id as string.
  
mapreduce/control.py