+ relationships = OneToMany('UserRelationship', inverse='user')
+ target_of_relationships = OneToMany('UserRelationship', inverse='target_user')
+
+ @classmethod
+ def is_valid_name(cls, name):
+ """Returns True iff the name is a valid username.
+
+ Only lowercase letters, numbers, and hyphens are allowed.
+
+ Names must also be at least one character long, but no more than 20,
+ and cannot start or end with a hyphen.
+ """
+ return re.match('^[-a-z0-9]{1,20}$', name) \
+ and name[0] != '-' and name[-1] != '-'