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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def run(self, job_name, handler_spec, input_reader_spec, output_writer_spec=None, params=None, shards=None, base_path=None):
 """Start a mapreduce job. Args: job_name: mapreduce name. Only for display purpose. handler_spec: fully qualified name to your map function/class. input_reader_spec: fully qualified name to input reader class. output_writer_spec: fully qualified name to output writer class. params: a dictionary of parameters for input reader and output writer initialization. shards: number of shards. This provides a guide to mapreduce. The real number of shards is determined by how input are splited. """

    if shards is None:
      shards = parameters.config.SHARD_COUNT
    if base_path is None:
      base_path = parameters.config.BASE_PATH
    mapreduce_id = control.start_map(
        job_name,
        handler_spec,
        input_reader_spec,
        params or {},
        mapreduce_parameters={
            "done_callback": self.get_callback_url(),
            "done_callback_method": "GET",
            "pipeline_id": self.pipeline_id,
            "base_path": base_path,
        },
        shard_count=shards,
        output_writer_spec=output_writer_spec,
        queue_name=self.queue_name,
        )
    self.fill(self.outputs.job_id, mapreduce_id)
    self.set_status(console_url="%s/detail?mapreduce_id=%s" % (
        (base_path, mapreduce_id)))