Make seekable True by default for arrow (#1186)

fsspec/implementations/arrow.py

@@ -157,7 +157,7 @@ def rm(self, path, recursive=False, maxdepth=None):
             self.fs.delete_file(path)
 
     @wrap_exceptions
-    def _open(self, path, mode="rb", block_size=None, seekable=False, **kwargs):
+    def _open(self, path, mode="rb", block_size=None, seekable=True, **kwargs):
         if mode == "rb":
             if seekable:
                 method = self.fs.open_input_file
@@ -202,6 +202,14 @@ def modified(self, path):
         path = self._strip_protocol(path)
         return self.fs.get_file_info(path).mtime
 
+    def cat_file(self, path, start=None, end=None, **kwargs):
+        kwargs["seekable"] = start not in [None, 0]
+        return super().cat_file(path, start=None, end=None, **kwargs)
+
+    def get_file(self, rpath, lpath, **kwargs):
+        kwargs["seekable"] = False
+        super().get_file(rpath, lpath, **kwargs)
+
 
 @mirror_from(
     "stream",

fsspec/implementations/tests/test_arrow.py

@@ -236,3 +236,8 @@ def test_seekable(fs, remote_dir):
     for seekable in [True, False]:
         with fs.open(remote_dir + "/a.txt", "rb", seekable=seekable) as file:
             assert file.seekable() == seekable
+            assert file.read() == data
+
+    with fs.open(remote_dir + "/a.txt", "rb", seekable=False) as file:
+        with pytest.raises(IOError):
+            file.seek(5)