Thanks for your answer @Joe and @pjnola, as you all suggested i referred flask-login docs
I found that we can customize the anonymous user class, so i customized for my requirement,
Anonymous class
#!/usr/bin/python
#flask-login anonymous user class
from flask.ext.login import AnonymousUserMixin
class Anonymous(AnonymousUserMixin):
def __init__(self):
self.username = 'Guest'
Then added this class to anonymous_user
login_manager.anonymous_user = Anonymous
From this it was able to fetch the username if it was anonymous request.