Unable to connect to cluster with 3.0.0a4 installed

Installed 3.0.0a4 and tried to execute the code from documentation here:

rom couchbase.cluster import Cluster
from couchbase_core.cluster import PasswordAuthenticator
cluster = Cluster('couchbase://10.112.192.101')
authenticator = PasswordAuthenticator('Administrator', 'password')
cluster.authenticate(authenticator)
cb = cluster.bucket('default')
cb_coll=cb.default_collection()
cb_coll.upsert('u:king_arthur',

{'name': 'Arthur', 'email': 'kingarthur@couchbase.com', 'interests': ['Holy Grail', 'African Swallows']}

)

1. OperationResult<RC=0x0, Key=u'u:king_arthur', CAS=0xb1da029b0000>

print(cb_coll.get('u:king_arthur').contentAs[str])

1. {u'interests': [u'Holy Grail', u'African Swallows'], u'name': u'Arthur', u'email': u'kingarthur@couchbase.com'}

1. 1. The CREATE PRIMARY INDEX step is only needed the first time you run this script
      cluster.query('CREATE PRIMARY INDEX ON default')

from couchbase_core.n1ql import N1QLQuery
row_iter = cluster.query(N1QLQuery('SELECT name FROM default WHERE ' + \
'$1 IN interests', 'African Swallows'))
for row in row_iter: print(row)

Throws the following error:

Traceback (most recent call last):
File "test-python3.py", line 3, in <module>
cluster = Cluster('couchbase://10.112.192.101')
File "/Users/a.senthilnathan/.pyenv/versions/3.6.8/lib/python3.6/site-packages/couchbase/cluster.py", line 100, in _init_
raise ArgumentError("Authenticator is mandatory")

I am using python 3.6.8