Accept mod in open_file_or_filename

satpy/readers/__init__.py

@@ -780,10 +780,10 @@ def _get_compression(file):
         return None
 
 
-def open_file_or_filename(unknown_file_thing):
+def open_file_or_filename(unknown_file_thing, mode="r"):
     """Try to open the *unknown_file_thing*, otherwise return the filename."""
     try:
-        f_obj = unknown_file_thing.open()
+        f_obj = unknown_file_thing.open(mode=mode)
     except AttributeError:
         f_obj = unknown_file_thing
     return f_obj

satpy/tests/test_readers.py

@@ -29,7 +29,7 @@
 
 from satpy.dataset.data_dict import get_key
 from satpy.dataset.dataid import DataID, ModifierTuple, WavelengthRange
-from satpy.readers import find_files_and_readers
+from satpy.readers import find_files_and_readers, open_file_or_filename
 
 # NOTE:
 # The following fixtures are not defined in this file, but are used and injected by Pytest:
@@ -1088,3 +1088,11 @@ def test_hash(self):
         assert len({hash(FSFile(fn, fs))
                     for fn in {self.local_filename, self.local_filename2}
                     for fs in [None, lfs, zfs, cfs]}) == 2*4
+
+
+def test_open_file_or_filename_uses_mode(tmp_path):
+    """Test that open_file_or_filename uses provided mode."""
+    with open(tmp_path / "hej", mode="wb") as fd:
+        fd.write(b"hej")
+    res = open_file_or_filename(tmp_path / "hej", mode="rb").read()
+    assert isinstance(res, bytes)