Align accepted filetypes with docstring description (#361)

* Align accepted filetypes with docstring description

* Fix upstream test

* Fix docstring to match function declaration

* Only guess filetype if not set

* Test ValueError on wrong filetype argument type

---------

Co-authored-by: Tom Nicholas <[email protected]>

Author: maxrjones

virtualizarr/backend.py

@@ -128,7 +128,7 @@ def open_virtual_dataset(
     ----------
     filepath : str, default None
         File path to open as a set of virtualized zarr arrays.
-    filetype : FileType, default None
+    filetype : FileType or str, default None
         Type of file to be opened. Used to determine which kerchunk file format backend to use.
         Can be one of {'netCDF3', 'netCDF4', 'HDF', 'TIFF', 'GRIB', 'FITS', 'dmrpp', 'zarr_v3', 'kerchunk'}.
         If not provided will attempt to automatically infer the correct filetype from header bytes.
@@ -182,13 +182,16 @@ def open_virtual_dataset(
     if backend and filetype:
         raise ValueError("Cannot pass both a filetype and an explicit VirtualBackend")
 
-    if filetype is not None:
-        # if filetype is user defined, convert to FileType
-        filetype = FileType(filetype)
-    else:
+    if filetype is None:
         filetype = automatically_determine_filetype(
             filepath=filepath, reader_options=reader_options
         )
+    elif isinstance(filetype, str):
+        # if filetype is a user defined string, convert to FileType
+        filetype = FileType(filetype.lower())
+    elif not isinstance(filetype, FileType):
+        raise ValueError("Filetype must be a valid string or FileType")
+
     if backend:
         backend_cls = backend
     else:

virtualizarr/tests/test_backend.py

@@ -383,9 +383,14 @@ def test_explicit_filetype(self, netcdf4_file):
         with pytest.raises(ValueError):
             open_virtual_dataset(netcdf4_file, filetype="unknown")
 
+        with pytest.raises(ValueError):
+            open_virtual_dataset(netcdf4_file, filetype=ManifestArray)
+
         with pytest.raises(NotImplementedError):
             open_virtual_dataset(netcdf4_file, filetype="grib")
 
+        open_virtual_dataset(netcdf4_file, filetype="netCDF4")
+
     def test_explicit_filetype_and_backend(self, netcdf4_file):
         with pytest.raises(ValueError):
             open_virtual_dataset(