fix #1378 and #1453

transformers/modeling_tf_distilbert.py

@@ -226,8 +226,9 @@ class TFMultiHeadSelfAttention(tf.keras.layers.Layer):
 
         dim_per_head = self.dim // self.n_heads
 
-        assert 2 <= len(tf.shape(mask)) <= 3
-        causal = (len(tf.shape(mask)) == 3)
+        mask_shape = shape_list(mask)
+        assert 2 <= len(mask_shape) <= 3
+        causal = (mask_shape) == 3)
         mask_reshape = [bs, 1, 1, k_length]
 
         def shape(x):