# user configures the universe domain:
client = Client(google.api_core.ClientOptions{universe_domain="foo.com"})

# api_endpoint points to the TPC universe:
api_endpoint = "service.foo.com"

# user does not configure the universe domain:
client = Client(google.api_core.ClientOptions{})

# api_endpoint defaults to GDU:
api_endpoint = "service.googleapis.com"