Python API design pattern question -

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i find have class instances descendants of other class instances, in tree fashion. example i'm making cms platform in python. might have realm, , under blog, , under post. each constructor takes it's parent first parameter knows belongs to. might this:

class realm(object):     def __init__(self, username, password)  class blog(object):     def __init__(self, realm, name)  class post(object);     def __init__(self, blog, title, body)

i typically add create method parent class, linkage bit more automatic. realm class might this:

class realm(object):     def __init__(self, username, password):         ...     def createblog(self, name):         return blog(self, name)

that allows user of api not import every single module, top level one. might like:

realm = realm("admin", "fds$#%") blog = realm.createblog("kittens!") post = blog.createpost("cute kitten", "some html blah blah")

the problem create methods redundant , have pydoc same parameters in 2 places.

i wonder if there's pattern (perhaps using metaclasses) linking 1 class instance parent class instance. way call code , have blog know it's parent realm is:

realm = realm("admin", "fds$#%") blog = realm.blog("kittens!")

you use common base class containers featuring add() method

class container(object):     def __init__(self, parent=none):         self.children = []         self.parent = parent     def add(self, child)         child.parent = self         self.children.append(child)         return child

and make parent parameter optional in derived classes

class blog(container):     def __init__(self, name, realm=none):         container.__init__(realm)         self.name = name

your code above read

realm = realm("admin", "fds$#%") blog = realm.add(blog("kittens!")) post = blog.add(post("cute kitten", "some html blah blah"))

you wouldn't have create...() methods more, no need document twice.

if setting parent involves more modifying parent attribute, use property or setter method.

edit: pointed out in comments below, children should tied parents end of contstructor. above approach can modified support this:

class container(object):     def __init__(self, parent=none):         self.children = []         self.parent = none     def add(self, cls, *args)         child = cls(self, *args)         self.children.append(child)         return child  class realm(container):     def __init__(self, username, password):         ...  class blog(container):     def __init__(self, realm, name):         ...  class post(container):     def __init__(self, blog, title, body):         ...  realm = realm("admin", "fds$#%") blog = realm.add(blog, "kittens!") post = blog.add(post, "cute kitten", "some html blah blah")

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