Slice of Openfiles should also be Opnfiles (#887)

Author: martindurant

fsspec/core.py

@@ -204,6 +204,12 @@ def __exit__(self, *args):
                     break
         [s.__exit__(*args) for s in self]
 
+    def __getitem__(self, item):
+        out = super().__getitem__(item)
+        if isinstance(item, slice):
+            return OpenFiles(out, mode=self.mode, fs=self.fs)
+        return out
+
     def __repr__(self):
         return "<List of %s OpenFile instances>" % len(self)
 

fsspec/tests/test_core.py

@@ -184,6 +184,8 @@ def test_multi_context(tmpdir):
     assert isinstance(files, OpenFiles)
     assert isinstance(files[0], OpenFile)
     assert len(files) == 2
+    assert isinstance(files[:1], OpenFiles)
+    assert len(files[:1]) == 1
     with files as of:
         assert len(of) == 2
         assert not of[0].closed