Flask BCrypt check_password_hash return False after saving via MongoEngine - mongodb

Question

I run into a weird situation, which is similar to this . This is my model:
class User(db.Document):
email = db.EmailField(required=True, unique=True)
username = db.StringField(max_length=50, required=True, unique=True )
password = db.StringField(required=True)
first_name = db.StringField(max_length=100, required=False)
last_name = db.StringField(max_length=100, required=False)
role = db.IntField(required = True, choices = role_choices, default = 5)
status = db.IntField(required = True, choices = status_choices, default = 1)
last_login = db.DateTimeField(required=False)
#property
def is_authenticated(self):
return True
#property
def is_active(self):
return True
#property
def is_anonymous(self):
return False
def __unicode__(self):
return self.username
def set_password(self, password):
self.password = bcrypt.generate_password_hash(password)
def __init__(self, *args, **kwargs):
username = kwargs.pop('username', None)
password = kwargs.pop('password', None)
email = kwargs.pop('email', None)
super(User, self).__init__(*args, **kwargs)
self.username = username
self.set_password(password)
self.email = email
meta = {
'allow_inheritance': False,
'indexes': ['-username'],
'ordering': ['-username']
}
def check_password(self, password):
return bcrypt.check_password_hash(self.password, password)
When I first create an instance of this User class, everything works as expected:
an = User(username="annguyen", first_name="An", last_name="Nguyen", password="janet78", email="an#gmail.com")
>>> an.password
'$2b$12$Ho9Q0/n4FPERytHKxA3szu8gzRZE4J9FxuZots8FFxJUKP6ULmqpe'
>>> an.save()
<User: annguyen>
>>> len(an.password)
60
>>> an.check_password('janet78')
True
However, when I retrieve this user from the database, the check_password method always return False.
>>> an_new = User.objects.get(username='annguyen')
>>> an_new.password
'$2b$12$j9VfNiySMKN19cYIEjuAseiamREUmGbB2ZFM4faoLJySB6uZfaCj2'
>>> len(an.password)
60
>>> len(an_new.password)
60
>>> an_new.check_password('janet78')
False
It is very clear that the password retrieved from the database is very different from what it was before being saved to the database, and therefore it always returns False. I spent a whole day trying to figure out what's wrong but couldn't come up with any clue. Can someone help point out how I can fix it.
I am developing on Windows 10 with Python 2.7, Flask 0.10.1, MongoDB 3.2, flask-mongoengine==0.7.5, mongoengine==0.10.6
Thanks a lot.