def create_user(nickname, email, password, gender):
"""Sign up a user"""
# check weather the email has been registered
assert UserHelper.get_by_email(email) is None
assert isinstance(nickname, basestring)
assert isinstance(email, basestring)
assert isinstance(password, basestring)
assert gender in [0, 1]
# Prepare password
salt = binascii.hexlify(os.urandom(32))
salted_password = UserHelper._password_hash(password, salt)
new_user = User()
new_user.nickname = nickname
new_user.email = email
new_user.salt = salt
new_user.salted_password = salted_password
new_user.gender = gender
new_user.save()
return new_user
