'module' object has no attribute 'unique'

[kennethgillen]

Following the instructions in the README (I think), I run the script and the following message appears:

(ghome) pi@raspberrypi:~/apps/GooglePyNotify $ python GooglePyNotify.py
Traceback (most recent call last):
  File "GooglePyNotify.py", line 5, in <module>
    import pychromecast
  File "/home/pi/venvs/ghome/local/lib/python2.7/site-packages/pychromecast/__init__.py", line 12, in <module>
    from .discovery import discover_chromecasts, start_discovery, stop_discovery
  File "/home/pi/venvs/ghome/local/lib/python2.7/site-packages/pychromecast/discovery.py", line 5, in <module>
    import zeroconf
  File "/home/pi/venvs/ghome/local/lib/python2.7/site-packages/zeroconf.py", line 152, in <module>
    @enum.unique
AttributeError: 'module' object has no attribute 'unique'
(ghome) pi@raspberrypi:~/apps/GooglePyNotify $

For reference:

(ghome) pi@raspberrypi:~/apps/GooglePyNotify $ git log | head
commit e8cd0fd6fc604a17949adf5c4410028ebc181743
Merge: f0bcf27 56668a6
Author: Elliott Cooper <33609461+GhostBassist@users.noreply.github.com>
Date:   Wed Jan 17 15:55:16 2018 +0000

    Merge pull request #3 from OldSchool4664/master

    Improve turnaround time for notifications

(ghome) pi@raspberrypi:~/apps/GooglePyNotify $ pip freeze
certifi==2018.4.16
chardet==3.0.4
enum==0.4.6
idna==2.6
netifaces==0.10.6
pkg-resources==0.0.0
protobuf==3.5.2.post1
PyChromecast==2.2.0
requests==2.18.4
six==1.11.0
urllib3==1.22
zeroconf==0.20.0