old_contents: # Copyright 2017, OpenCensus Authors
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  import time
  
  from opencensus.trace import execution_context
  from opencensus.trace.exporters import print_exporter
  from opencensus.trace.tracers import Tracer
  from opencensus.trace.samplers import always_on
  
  
  def function_to_trace():
      time.sleep(1)
  
  
  def main():
      sampler = always_on.AlwaysOnSampler()
      exporter = print_exporter.PrintExporter()
      tracer = Tracer(sampler=sampler, exporter=exporter)
  
      with tracer.span(name='root') as root_span:
          tracer.add_label_to_current_span(label_key='example key',
                                           label_value='example value')
          function_to_trace()
          with tracer.span(name='child') as child_span:
              function_to_trace()
  
      # Get the current tracer
      tracer = execution_context.get_opencensus_tracer()
  
      # Explicitly create spans
      tracer.start_span()
  
      # Get current span
      cur_span = execution_context.get_current_span()
  
      # Explicitly end span
      tracer.end_span()
  
  
  if __name__ == '__main__':
      main()
  
new_contents: # Copyright 2017, OpenCensus Authors
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  
  import time
  
  from opencensus.trace import execution_context
  from opencensus.trace.exporters import print_exporter
  from opencensus.trace.tracer import Tracer
  from opencensus.trace.samplers import always_on
  
  
  def function_to_trace():
      time.sleep(1)
  
  
  def main():
      sampler = always_on.AlwaysOnSampler()
      exporter = print_exporter.PrintExporter()
      tracer = Tracer(sampler=sampler, exporter=exporter)
  
      with tracer.span(name='root') as root_span:
          tracer.add_attribute_to_current_span(attribute_key='example key',
                                               attribute_value='example value')
          function_to_trace()
          with tracer.span(name='child') as child_span:
              function_to_trace()
  
      # Get the current tracer
      tracer = execution_context.get_opencensus_tracer()
  
      # Explicitly create spans
      tracer.start_span()
  
      # Get current span
      cur_span = execution_context.get_current_span()
  
      # Explicitly end span
      tracer.end_span()
  
  
  if __name__ == '__main__':
      main()
  
subject: Update the hello world example (#102)