z3c.objpath 1.3

ObjectPath

This package contains two things:

• the z3c.objpath.interfaces.IObjectPath interface.

• some helper functions to construct (relative) object paths, in z3c.objpath.path.

The idea is that a particular application can implement a utility that fulfills the IObjectPath interface, so that it is possible to construct paths to objects in a uniform way. The implementation may be done with zope.traversing, but in some cases you want application-specific object paths. In this case, the functions in z3c.objpath.path might be useful.

We’ll have a simple item:

>>> class Item(object):
...   __name__ = None
...   __parent__ = None
...   def __repr__(self):
...     return '<Item %s>' % self.__name__

Let’s create a simple container-like object:

>>> class Container(Item):
...   def __init__(self):
...     self._d = {}
...   def __setitem__(self, name, obj):
...     self._d[name] = obj
...     obj.__name__ = name
...     obj.__parent__ = self
...   def __getitem__(self, name):
...     return self._d[name]
...   def __repr__(self):
...     return '<Container %s>' % self.__name__

Now let’s create a structure:

>>> root = Container()
>>> root.__name__ = 'root'
>>> data = root['data'] = Container()
>>> a = data['a'] = Container()
>>> b = data['b'] = Container()
>>> c = data['c'] = Item()
>>> d = a['d'] = Item()
>>> e = a['e'] = Container()
>>> f = e['f'] = Item()
>>> g = b['g'] = Item()

We will now exercise two functions, path and resolve, which are inverses of each other:

>>> from z3c.objpath import path, resolve

We can create a path to a from root:

>>> path(root, a)
'/root/data/a'

We can also resolve it again:

>>> resolve(root, '/root/data/a')
<Container a>

We can also create a path to a from data:

>>> path(data, a)
'/data/a'

And resolve it again:

>>> resolve(data, '/data/a')
<Container a>

We can make a deeper path:

>>> path(root, f)
'/root/data/a/e/f'

And resolve it:

>>> resolve(root, '/root/data/a/e/f')
<Item f>

The path ‘/’ leads to the root object:

>>> resolve(root, '/')
<Container root>

We get an error if we cannot construct a path:

>>> path(e, a)
Traceback (most recent call last):
 ...
ValueError: Cannot create path for <Container a>

We also get an error if we cannot resolve a path:

>>> resolve(root, '/root/data/a/f/e')
Traceback (most recent call last):
 ...
ValueError: Cannot resolve path /root/data/a/f/e

z3c.objpath changes