Raise a clearer error when open_dataset is given a list of paths

doc/whats-new.rst

@@ -49,6 +49,10 @@ Deprecations
 Bug Fixes
 ~~~~~~~~~
 
+- :py:func:`~xarray.open_dataset` now raises an error pointing at
+  :py:func:`~xarray.open_mfdataset` when it is given a list or tuple of paths,
+  instead of reporting that no IO backend matched the input (:issue:`6510`).
+  By `NoiceHex <https://github.com/NoiceHax>`_.
 - Fix async zarr tests using ``wraps`` with ``autospec=True`` on async methods,
   which caused ``AsyncMock`` objects to leak through instead of real array data
   (:pull:`11232`).

pyproject.toml

@@ -424,6 +424,7 @@ Claus = "Claus"
 Celles = "Celles"
 slowy = "slowy"
 Commun = "Commun"
+Noice = "Noice"
 
 # Tests
 Ome = "Ome"

xarray/backends/plugins.py

@@ -214,6 +214,12 @@ def guess_engine(
         if not is_remote_uri(store_spec_str) and not os.path.exists(store_spec_str):
             raise FileNotFoundError(f"No such file: '{store_spec_str}'")
 
+    if isinstance(store_spec, list | tuple):
+        raise ValueError(
+            f"open_dataset opens a single file, but got a {type(store_spec).__name__}. "
+            "Use open_mfdataset to open multiple files as a single dataset."
+        )
+
     raise ValueError(error_msg)
 
 

xarray/tests/test_plugins.py

@@ -250,6 +250,16 @@ def test_guess_engine_file_not_found() -> None:
         plugins.guess_engine("https://example.com/missing.h5")
 
 
+@mock.patch(
+    "xarray.backends.plugins.list_engines",
+    mock.MagicMock(return_value={"dummy": DummyBackendEntrypointArgs()}),
+)
+@pytest.mark.parametrize("paths", [["a.nc", "b.nc"], ("a.nc", "b.nc")])
+def test_guess_engine_sequence_of_paths(paths) -> None:
+    with pytest.raises(ValueError, match=r"Use open_mfdataset"):
+        plugins.guess_engine(paths)
+
+
 @pytest.mark.parametrize("engine", common.BACKEND_ENTRYPOINTS.keys())
 def test_get_backend_fastpath_skips_list_engines(engine: str) -> None:
     """Test that built-in engines skip list_engines (fastpath)."""