add pt2tf tool

pt2tf/onnx-tensorflow/onnx_tf/handlers/backend/pad_mixin.py

@@ -0,0 +1,17 @@
+import numpy as np
+import tensorflow as tf
+
+
+class PadMixin(object):
+
+  @classmethod
+  def get_padding_as_op(cls, x, pads):
+    num_dim = int(len(pads) / 2)
+
+    tf_pads = np.transpose(np.array(pads).reshape([2, num_dim]))
+    tf_pads = [0, 0, 0, 0] + tf_pads.flatten().tolist()
+
+    padding = tf.constant(
+        np.array(tf_pads).reshape([num_dim + 2, 2])
+        .astype(np.int32))  # tf requires int32 paddings
+    return tf.pad(x, padding)