fix pylint

Author: nbcsm

tf2onnx/convert.py

@@ -10,7 +10,6 @@
 from __future__ import unicode_literals
 
 import argparse
-import onnx
 from onnx import helper
 import tensorflow as tf
 

tf2onnx/graph.py

@@ -87,6 +87,7 @@ def attr(self):
 
     @property
     def attr_onnx(self):
+        """Return onnx valid attributes"""
         schema = get_schema(self.type, self.graph.opset, self.domain)
         if schema is None and not (self.is_const() or self.is_graph_input()):
             log.warning("Node %s uses non-stardard onnx op <%s, %s>, skip attribute check", self.name, self.domain,