ZeroDivisionError: float division by zero

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How to fix this issue. I followed this video here

This full code:

#!/usr/bin/env python
import rospy

from std_msgs.msg import String


rate1 = 30
rate2 = 1
msg1 = "30 hz"
msg2 = "1 hz"

def callbsck1(event):
  pub_1.publish(msg1)

def callbsck2(event):
  pub_2.publish(msg2)

if __name__ == '__main__':
  rospy.init_node('async_publish')
  pub_1 = rospy.Publisher ('topic1', String, queue_size=10)
  pub_2 = rospy.Publisher('topic2', String, queue_size=10)
  rospy.Timer(rospy.Duration(1/rate1), callbsck1)
  rospy.Timer(rospy.Duration(1 / rate2), callbsck2)
  rospy.spin()

This error:

Exception in thread Thread-5:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rospy/timer.py", line 221, in run
    r = Rate(1.0 / self._period.to_sec(), reset=self._reset)
ZeroDivisionError: float division by zero