diff --git a/python/gtsam/imuBias.py b/python/gtsam/imuBias.py
index 1cb367b9f..399cefb98 100644
--- a/python/gtsam/imuBias.py
+++ b/python/gtsam/imuBias.py
@@ -1 +1,4 @@
+# This trick is to allow direct import of sub-modules
+# without this, we can only do `from gtsam.gtsam.imuBias import X`
+# with this trick, we can do `from gtsam.imuBias import X`
 from .gtsam.imuBias import *
diff --git a/python/gtsam/noiseModel.py b/python/gtsam/noiseModel.py
index 9b1929a8e..6e1b43488 100644
--- a/python/gtsam/noiseModel.py
+++ b/python/gtsam/noiseModel.py
@@ -1 +1,4 @@
+# This trick is to allow direct import of sub-modules
+# without this, we can only do `from gtsam.gtsam.noiseModel import X`
+# with this trick, we can do `from gtsam.noiseModel import X`
 from .gtsam.noiseModel import *
\ No newline at end of file
diff --git a/python/gtsam/symbol_shorthand.py b/python/gtsam/symbol_shorthand.py
index 956ed693a..748d36558 100644
--- a/python/gtsam/symbol_shorthand.py
+++ b/python/gtsam/symbol_shorthand.py
@@ -1 +1,4 @@
+# This trick is to allow direct import of sub-modules
+# without this, we can only do `from gtsam.gtsam.symbol_shorthand import X`
+# with this trick, we can do `from gtsam.symbol_shorthand import X`
 from .gtsam.symbol_shorthand import *
\ No newline at end of file