Pushover does not work on my mac with Maveric #29

When I use pushover in a python script in windows and linux it works fine, but when I run the same script on my mac I get this error message:
attributeerror module pushover does not have an attribute Client.
I tried to reinstall pushover , but it does not help..
What can be wrong?
The python environment on the mac is setup similar to the windows and linux environments.
And the python version is 3.7