add _id property to GridFile instances

gridfs/grid_file.py

@@ -164,6 +164,12 @@ class GridFile(object):
 
         self.__collection.chunks.remove({"files_id": self.__id})
 
+    @property
+    def _id(self):
+        """Get the value of ``"_id"`` for this :class:`GridFile`.
+        """
+        return self.__id
+
     @property
     def closed(self):
         """Is this :class:`GridFile` closed?

test/test_grid_file.py

@@ -426,6 +426,10 @@ class TestGridFile(unittest.TestCase):
 
         self.assertEqual(in_data, out_data)
 
+    def test_id(self):
+        file = GridFile({"_id": "test"}, self.db, "w")
+        self.assertEqual("test", file._id)
+
 
 if __name__ == "__main__":
     unittest.main()