[BugFix] Fix is_memmap attribute for memmap_like and memmap (#625)

tensordict/_td.py

@@ -1679,6 +1679,11 @@ def _populate(
             self._is_memmap = True
             self._is_shared = False  # since they are mutually exclusive
             self._device = torch.device("cpu")
+        else:
+            dest._is_memmap = True
+            dest._is_shared = False  # since they are mutually exclusive
+            dest._device = torch.device("cpu")
+
         dest._is_locked = True
         return dest
 

test/test_tensorclass.py

@@ -1735,6 +1735,7 @@ class MyClass:
         assert isinstance(cmemmap.x, MemoryMappedTensor)
         assert isinstance(cmemmap.y.x, MemoryMappedTensor)
         assert cmemmap.z == "foo"
+        assert cmemmap.is_memmap()
 
 
 class TestNesting:

test/test_tensordict.py

@@ -2848,6 +2848,7 @@ def test_memmap_like(self, td_name, device, use_dir, tmpdir, num_threads):
         for key in td.keys(True):
             assert td[key] is not tdmemmap[key]
         assert (tdmemmap == 0).all()
+        assert tdmemmap.is_memmap()
 
     def test_memmap_prefix(self, td_name, device, tmp_path):
         if td_name == "memmap_td":
@@ -6158,6 +6159,7 @@ def test_memmap_like(self, tmpdir):
         )
         tdm = td.memmap_like(prefix=tmpdir)
         assert tdm.names == ["a", "b", "c", "d"]
+        assert tdm.is_memmap()
 
     def test_memmap_td(self):
         td = self.memmap_td("cpu")