code: def tracer_config(__init__, app, args, kwargs):
      
      __init__(*args, **kwargs)
  
      tracing = app.settings.get('opentracing_tracing')
      tracer_callable = app.settings.get('opentracing_tracer_callable')
      tracer_parameters = app.settings.get('opentracing_tracer_parameters', {})
  
      if tracer_callable is not None:
          if not callable(tracer_callable):
              tracer_callable = _get_callable_from_name(tracer_callable)
  
          tracer = tracer_callable(**tracer_parameters)
          tracing = TornadoTracing(tracer)
  
      if tracing is None:
          tracing = TornadoTracing()  # fallback to the global tracer
  
      app.settings['opentracing_tracing'] = tracing
  
      tracing._trace_all = app.settings.get('opentracing_trace_all',
                                            DEFAULT_TRACE_ALL)
      tracing._trace_client = app.settings.get('opentracing_trace_client',
                                               DEFAULT_TRACE_CLIENT)
      tracing._start_span_cb = app.settings.get('opentracing_start_span_cb',
                                                None)
  
      httpclient._set_tracing_enabled(tracing._trace_client)
      if tracing._trace_client:
          httpclient._set_tracing_info(tracing._tracer_obj,
                                       tracing._start_span_cb)
docs: Wraps the Tornado web application initialization so that the
      TornadoTracing instance is created around an OpenTracing-compatible tracer.