code: def _paths_from_env(variable: str, default: List[Path]) -> List[Path]:
      
      # TODO(srstevenson): Use assignment expression in Python 3.8.
      value = os.environ.get(variable)
      if value:
          return [Path(path) for path in value.split(":")]
      return default
docs: Read an environment variable as a list of paths.
  
      The environment variable with the specified name is read, and its
      value split on colons and returned as a list of paths. If the
      environment variable is not set, or set to the empty string, the
      default value is returned.
  
      Parameters
      ----------
      variable : str
          Name of the environment variable.
      default : List[Path]
          Default value.
  
      Returns
      -------
      List[Path]
          Value from environment or default.