code: def get_default_path_config():
      
      if 'SAWTOOTH_HOME' in os.environ:
          home_dir = os.environ['SAWTOOTH_HOME']
          return PathConfig(
              config_dir=os.path.join(home_dir, 'etc'),
              log_dir=os.path.join(home_dir, 'logs'),
              data_dir=os.path.join(home_dir, 'data'),
              key_dir=os.path.join(home_dir, 'keys'),
              policy_dir=os.path.join(home_dir, 'policy'))
  
      if os.name == 'nt':
          # Paths appropriate for Windows.
          base_dir = \
              os.path.dirname(os.path.dirname(os.path.abspath(sys.argv[0])))
          return PathConfig(
              config_dir=os.path.join(base_dir, 'conf'),
              log_dir=os.path.join(base_dir, 'logs'),
              data_dir=os.path.join(base_dir, 'data'),
              key_dir=os.path.join(base_dir, 'conf', 'keys'),
              policy_dir=os.path.join(base_dir, 'policy'))
  
      # Paths appropriate for modern Linux distributions.
      return PathConfig(
          config_dir='/etc/sawtooth',
          log_dir='/var/log/sawtooth',
          data_dir='/var/lib/sawtooth',
          key_dir='/etc/sawtooth/keys',
          policy_dir='/etc/sawtooth/policy')
docs: Returns the default PathConfig as calculated based on SAWTOOTH_HOME
      (if set) and operating system.