diff --git a/.flake8 b/.flake8
index 8285441..eb09e54 100644
--- a/.flake8
+++ b/.flake8
@@ -5,6 +5,7 @@ exclude =
   .git,
   build,
   build_release,
+  cmake/cmake_extension.py,
   kaldifeat/python/kaldifeat/__init__.py
 
 ignore =
diff --git a/kaldifeat/python/kaldifeat/__init__.py b/kaldifeat/python/kaldifeat/__init__.py
index 60c6443..ea39003 100644
--- a/kaldifeat/python/kaldifeat/__init__.py
+++ b/kaldifeat/python/kaldifeat/__init__.py
@@ -10,5 +10,7 @@ from _kaldifeat import (
 
 from .fbank import Fbank, OnlineFbank
 from .mfcc import Mfcc, OnlineMfcc
+from .offline_feature import OfflineFeature
+from .online_feature import OnlineFeature
 from .plp import OnlinePlp, Plp
 from .spectrogram import Spectrogram
diff --git a/kaldifeat/python/kaldifeat/online_feature.py b/kaldifeat/python/kaldifeat/online_feature.py
index cf687cf..2acf67f 100644
--- a/kaldifeat/python/kaldifeat/online_feature.py
+++ b/kaldifeat/python/kaldifeat/online_feature.py
@@ -91,5 +91,15 @@ class OnlineFeature(object):
         """
         self.computer.input_finished()
 
+    @property
+    def dim(self) -> int:
+        """Return the feature dimension of this extractor"""
+        return self.computer.dim
+
+    @property
+    def frame_shift_in_seconds(self) -> int:
+        """Return frame shift in seconds of this extractor"""
+        return self.computer.frame_shift_in_seconds
+
     def __getstate__(self):
         return self.opts.as_dict()