code: def lint(session):
      
      session.interpreter = 'python3.6'
      session.install('flake8')
  
      # Install dev packages.
      _install_dev_packages(session)
  
      session.run(
          'flake8',
          '--exclude=contrib/opencensus-ext-ocagent/opencensus/ext/ocagent/trace_exporter/gen/',
          'context/', 'contrib/', 'opencensus/', 'tests/', 'examples/')
docs: Run flake8.
      Returns a failure if flake8 finds linting errors or sufficiently
      serious code quality issues.