Please follow steps below.
$ python3 -m venv venv
$ source venv/bin/activate
$ pip install protobuf
# or just: pip install protobuf
$ brew install protobuf
$ which protoc
$ protoc --python_out=. addressbook.proto
$ python add_person.py addressbook
addressbook: File not found. Creating a new file.
Enter person ID number: 7
Enter name: James Bond
Enter email address (blank for none): 007@mi6
Enter a phone number (or leave blank to finish): 007007
Is this a mobile, home, or work phone? mobile
Enter a phone number (or leave blank to finish):
$ python list_people.py addressbook
Person ID: 7
Name: James Bond
E-mail address: 007@mi6
Mobile phone #: 007007