more Python 3 compatibility (#1796)

* keep subscribers around

* more subprocess decode

* add another seek(0), remove an unncessary one

test/test_rospy/nodes/listener.py

@@ -55,7 +55,7 @@ def listener():
     # run simultaenously.
     rospy.init_node('listener', anonymous=True)
 
-    rospy.Subscriber("chatter", String, callback)
+    sub = rospy.Subscriber("chatter", String, callback)
 
     # spin() simply keeps python from exiting until this node is stopped
     rospy.spin()

test/test_rospy/test/rostest/test_topic_statistics.py

@@ -74,7 +74,7 @@ def frequency_acceptable(self, topic, expected, error_margin=0.1):
         return abs(found_freq - expected) / expected <= error_margin
 
     def test_frequencies(self):
-        rospy.Subscriber('/statistics', TopicStatistics, self.new_msg)
+        sub = rospy.Subscriber('/statistics', TopicStatistics, self.new_msg)
 
         self.assert_eventually(
             lambda: '/very_fast_chatter' in self.topic_statistic_msg_map)

test/test_rospy/test/unit/test_rospy_msg.py

@@ -199,6 +199,7 @@ def validate_vals(vals, teststrs=teststrs):
 
         #deserialize with extra data leftover
         b.truncate(0)
+        b.seek(0)
         b.write(valids[0]+b'leftovers')
         rospy.msg.deserialize_messages(b, msg_queue, data_class)
         self.assertEquals(1, len(msg_queue))
@@ -224,7 +225,6 @@ def validate_vals(vals, teststrs=teststrs):
         #deserialize multiple values with max_msgs
         max_msgs = 5
         b.truncate(0)
-        b.seek(0)
         for v in valids:
             b.write(v)
         rospy.msg.deserialize_messages(b, msg_queue, data_class, max_msgs=max_msgs)

utilities/roswtf/test/check_roswtf_command_line_online.py

@@ -64,7 +64,7 @@ def setUp(self):
     ## test that the rosmsg command works
     def test_cmd_help(self):
         cmd = 'roswtf'
-        output = Popen([cmd, '-h'], stdout=PIPE).communicate()[0]
+        output = Popen([cmd, '-h'], stdout=PIPE).communicate()[0].decode()
         self.assert_('Options' in output)
 
     def test_offline(self):
@@ -117,12 +117,12 @@ def test_offline(self):
         # every package in the ROS stack, which doesn't work.
 
         output, err = Popen([cmd], **kwds).communicate()
-        self._check_output([cmd], output, err)
+        self._check_output([cmd], output.decode(), err.decode())
 
         # run roswtf on a simple launch file online
         rospack = rospkg.RosPack()
         p = os.path.join(rospack.get_path('roswtf'), 'test', 'min.launch')
-        output = Popen([cmd, p], **kwds).communicate()[0]
+        output = Popen([cmd, p], **kwds).communicate()[0].decode()
         self._check_output([cmd, p], output)
 
     def _check_output(self, cmd, output, error=None):