[BugFix] Check if the current user has write access (#781)

tensordict/memmap.py

@@ -9,7 +9,6 @@
 
 import mmap
 import os
-import stat
 
 import sys
 import tempfile
@@ -1073,7 +1072,6 @@ def _chunk(input, chunks, dim=0):
 def _is_writable(file_path):
     file_path = str(file_path)
     if os.path.exists(file_path):
-        st = os.stat(file_path)
-        return bool(st.st_mode & (stat.S_IWUSR | stat.S_IWGRP | stat.S_IWOTH))
+        return os.access(file_path, os.W_OK)
     # Assume that the file can be written in the directory
     return True

test/test_memmap.py

@@ -718,6 +718,7 @@ def test_save_td_with_nested(self, tmpdir):
 
 
 class TestReadWrite:
+    @pytest.mark.skipif(os.getuid() == 0, reason="root can write to read-only files")
     def test_read_only(self, tmpdir):
         tmpdir = Path(tmpdir)
         file_path = tmpdir / "elt.mmap"
@@ -747,6 +748,7 @@ def test_read_only(self, tmpdir):
         assert (mmap.reshape(-1) == torch.arange(6)).all()
 
     @pytest.mark.skipif(not HAS_NESTED_TENSOR, reason="Nested tensor incomplete")
+    @pytest.mark.skipif(os.getuid() == 0, reason="root can write to read-only files")
     def test_read_only_nested(self, tmpdir):
         tmpdir = Path(tmpdir)
         file_path = tmpdir / "elt.mmap"