How to use the opencensus.trace.tracer.Tracer function in opencensus

def test_should_sample_force_not_trace(self):

        span_context = mock.Mock()
        span_context.trace_options.enabled = False
        sampler = mock.Mock()
        sampler.should_sample.return_value = False
        tracer = tracer_module.Tracer(
            span_context=span_context, sampler=sampler)
        sampled = tracer.should_sample()

        self.assertFalse(sampled)

def test_get_tracer_context_tracer(self):
        from opencensus.trace.tracers import context_tracer

        sampler = mock.Mock()
        sampler.should_sample.return_value = True
        tracer = tracer_module.Tracer(sampler=sampler)

        result = tracer.get_tracer()

        assert isinstance(result, context_tracer.ContextTracer)
        self.assertTrue(tracer.span_context.trace_options.enabled)

def test_finish_not_sampled(self):
        from opencensus.trace.tracers import noop_tracer

        sampler = mock.Mock()
        sampler.should_sample.return_value = False
        span_context = mock.Mock()
        span_context.trace_options.enabled = False
        tracer = tracer_module.Tracer(
            span_context=span_context, sampler=sampler)
        assert isinstance(tracer.tracer, noop_tracer.NoopTracer)
        mock_tracer = mock.Mock()
        tracer.tracer = mock_tracer
        tracer.finish()
        self.assertTrue(mock_tracer.finish.called)

def create_tracer(span_context=None):
    return tracer_module.Tracer(
        span_context=span_context,
        sampler=get_tracer_sampler(),
        exporter=get_tracer_exporter(),
        propagator=get_tracer_propagator())

def _before_request(self):
        """A function to be run before each request.

        See: http://flask.pocoo.org/docs/0.12/api/#flask.Flask.before_request
        """
        # Do not trace if the url is blacklisted
        if utils.disable_tracing_url(flask.request.url, self.blacklist_paths):
            return

        try:
            span_context = self.propagator.from_headers(flask.request.headers)

            tracer = tracer_module.Tracer(
                span_context=span_context,
                sampler=self.sampler,
                exporter=self.exporter,
                propagator=self.propagator)

            span = tracer.start_span()
            span.span_kind = span_module.SpanKind.SERVER
            # Set the span name as the name of the current module name
            span.name = '[{}]{}'.format(
                flask.request.method,
                flask.request.url)
            tracer.add_attribute_to_current_span(
                HTTP_HOST, flask.request.host
            )
            tracer.add_attribute_to_current_span(
                HTTP_METHOD, flask.request.method

def __call__(self, *args, **kwargs):
        kwds = kwargs.pop("kwds")

        span_context_binary = kwargs.pop("span_context_binary")
        propagator = binary_format.BinaryFormatPropagator()
        kwargs["span_context"] = propagator.from_header(span_context_binary)

        _tracer = tracer.Tracer(**kwargs)
        execution_context.set_opencensus_tracer(_tracer)
        with _tracer.span(name=threading.current_thread().name):
            result = self.func(*args, **kwds)
        execution_context.clean()
        return result

import grpc

import demo_pb2
import demo_pb2_grpc

from logger import getJSONLogger
logger = getJSONLogger('emailservice-client')

from opencensus.trace.tracer import Tracer
from opencensus.trace.exporters import stackdriver_exporter
from opencensus.trace.ext.grpc import client_interceptor

try:
    exporter = stackdriver_exporter.StackdriverExporter()
    tracer = Tracer(exporter=exporter)
    tracer_interceptor = client_interceptor.OpenCensusClientInterceptor(tracer, host_port='0.0.0.0:8080')
except:
    tracer_interceptor = client_interceptor.OpenCensusClientInterceptor()

def send_confirmation_email(email, order):
  channel = grpc.insecure_channel('0.0.0.0:8080')
  channel = grpc.intercept_channel(channel, tracer_interceptor)
  stub = demo_pb2_grpc.EmailServiceStub(channel)
  try:
    response = stub.SendOrderConfirmation(demo_pb2.SendOrderConfirmationRequest(
      email = email,
      order = order
    ))
    logger.info('Request sent.')
  except grpc.RpcError as err:
    logger.error(err.details())

def _before_request(self, request):
        if utils.disable_tracing_url(request.path, self._blacklist_paths):
            return

        try:
            span_context = self.propagator.from_headers(request.headers)

            tracer = tracer_module.Tracer(
                span_context=span_context,
                sampler=self.sampler,
                exporter=self.exporter,
                propagator=self.propagator)

            span = tracer.start_span()

            # Set the span name as the name of the current module name
            span.name = '[{}]{}'.format(
                request.method,
                request.path)

            span.span_kind = span_module.SpanKind.SERVER
            tracer.add_attribute_to_current_span(
                attribute_key=HTTP_HOST,
                attribute_value=request.host_url)

def initialize_tracer(project_id):
    exporter = stackdriver_exporter.StackdriverExporter(
        project_id=project_id
    )
    tracer = opencensus.trace.tracer.Tracer(exporter=exporter)

    return tracer
# [END trace_setup_python_configure]