Make pathlib extensible

brettcannon · March 1, 2023, 1:17am

The key thing is os.fspath() prevents you from accidentally calling str() on a non-path-like object like None.

python/cpython/blob/7d1d66341838d7d1963c9ee7ffca2950d3a751fd/Lib/os.py#L1057


      
          path representation is not str or bytes, TypeError is raised. If the
          provided path is not str, bytes, or os.PathLike, TypeError is raised.
          """
          if isinstance(path, (str, bytes)):
              return path
          
          # Work from the object's type to match method resolution of other magic
          # methods.
          path_type = type(path)
          try:
              path_repr = path_type.__fspath__(path)
          except AttributeError:
              if hasattr(path_type, '__fspath__'):
                  raise
              else:
                  raise TypeError("expected str, bytes or os.PathLike object, "
                                  "not " + path_type.__name__)
          if isinstance(path_repr, (str, bytes)):
              return path_repr
          else:
              raise TypeError("expected {}.__fspath__() to return str or bytes, "

The idea is that the string representation is like an encoding of a path just like some integer can be an encoding for a Unicode code point, and thus not something to directly think about if you’re using pathlib.