diff --git a/ppocr/losses/det_basic_loss.py b/ppocr/losses/det_basic_loss.py
index eba5526dd2bd1c0328130b50817172df437cc360..d11d5ef7ddcc870f2811a29391a632dc62574a6b 100644
--- a/ppocr/losses/det_basic_loss.py
+++ b/ppocr/losses/det_basic_loss.py
@@ -11,7 +11,10 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
+"""
+This code is refer from:
+https://github.com/WenmuZhou/DBNet.pytorch/blob/master/models/losses/basic_loss.py
+"""
 from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
diff --git a/ppocr/losses/det_db_loss.py b/ppocr/losses/det_db_loss.py
index b079aabff7c7deccc7e365b91c9407f7e894bcb9..708ffbdb47f349304e2bfd781a836e79348475f4 100755
--- a/ppocr/losses/det_db_loss.py
+++ b/ppocr/losses/det_db_loss.py
@@ -11,6 +11,10 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+"""
+This code is refer from:
+https://github.com/WenmuZhou/DBNet.pytorch/blob/master/models/losses/DB_loss.py
+"""
 
 from __future__ import absolute_import
 from __future__ import division
diff --git a/ppocr/modeling/transforms/tps.py b/ppocr/modeling/transforms/tps.py
index dcce6246ac64b4b84229cbd69a4dc53c658b4c7b..9bdab0f85112b90d8da959dce4e258188a812052 100644
--- a/ppocr/modeling/transforms/tps.py
+++ b/ppocr/modeling/transforms/tps.py
@@ -11,6 +11,10 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+"""
+This code is refer from:
+https://github.com/clovaai/deep-text-recognition-benchmark/blob/master/modules/transformation.py
+"""
 
 from __future__ import absolute_import
 from __future__ import division
@@ -231,7 +235,8 @@ class GridGenerator(nn.Layer):
         """ Return inv_delta_C which is needed to calculate T """
         F = self.F
         hat_eye = paddle.eye(F, dtype='float64')  # F x F
-        hat_C = paddle.norm(C.reshape([1, F, 2]) - C.reshape([F, 1, 2]), axis=2) + hat_eye
+        hat_C = paddle.norm(
+            C.reshape([1, F, 2]) - C.reshape([F, 1, 2]), axis=2) + hat_eye
         hat_C = (hat_C**2) * paddle.log(hat_C)
         delta_C = paddle.concat(  # F+3 x F+3
             [