Fix snapshotter ordering (#2327)

Author: krzentner

src/garage/experiment/snapshotter.py

@@ -159,7 +159,7 @@ def load(self, load_dir, itr='last'):
                     raise FileNotFoundError(errno.ENOENT,
                                             os.strerror(errno.ENOENT),
                                             '*.pkl file in', load_dir)
-                files.sort()
+                files.sort(key=_extract_snapshot_itr)
                 load_from_file = files[0] if itr == 'first' else files[-1]
                 load_from_file = os.path.join(load_dir, load_from_file)
 
@@ -170,5 +170,20 @@ def load(self, load_dir, itr='last'):
             return cloudpickle.load(file)
 
 
+def _extract_snapshot_itr(filename: str) -> int:
+    """Extracts the integer itr from a filename.
+
+    Args:
+        filename(str): The snapshot filename.
+
+    Returns:
+        int: The snapshot as an integer.
+
+    """
+    base = os.path.splitext(filename)[0]
+    digits = base.split('itr_')[1]
+    return int(digits)
+
+
 class NotAFileError(Exception):
     """Raise when the snapshot is not a file."""

tests/garage/experiment/test_snapshotter.py

@@ -22,6 +22,7 @@
 class TestSnapshotter:
 
     def setup_method(self):
+        # pylint: disable=consider-using-with
         self.temp_dir = tempfile.TemporaryDirectory()
 
     def teardown_method(self):
@@ -78,3 +79,10 @@ def test_conflicting_params(self):
             Snapshotter(snapshot_dir=self.temp_dir.name,
                         snapshot_mode='gap_overwrite',
                         snapshot_gap=1)
+
+    def test_sorts_correctly(self):
+        snapshotter = Snapshotter(self.temp_dir.name, 'all', 2)
+        snapshotter.save_itr_params(80, {'test_itr': 80})
+        snapshotter.save_itr_params(120, {'test_itr': 120})
+        last = snapshotter.load(self.temp_dir.name)
+        assert last['test_itr'] == 120