[Data] Improve _resolve_paths_and_filesystem error message (ray-pro…

…ject#38366)

If you pass an invalid input to _resolve_paths_and_filesystem, you get an error message telling you what types are valid, but it doesn't tell you what you passed it.

> paths must be a path string or a list of path strings.

This PR updates the error message to describe what you passed in:

> 'Expected paths to be a str, pathlib.Path, or list[str], but got None'

Signed-off-by: Balaji Veeramani <[email protected]>

python/ray/data/datasource/file_based_datasource.py

@@ -663,7 +663,10 @@ def _resolve_paths_and_filesystem(
  if isinstance(paths, pathlib.Path):
  paths = [str(paths)]
  elif not isinstance(paths, list) or any(not isinstance(p, str) for p in paths):
- raise ValueError("paths must be a path string or a list of path strings.")
+ raise ValueError(
+ "Expected `paths` to be a `str`, `pathlib.Path`, or `list[str]`, but got "
+ f"`{paths}`."
+ )
  elif len(paths) == 0:
  raise ValueError("Must provide at least one path.")