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=========================
23: Traversal Hierarchies
=========================
Objects with subobjects and views, all via URLs.
Background
==========
In :doc:`../traversal_siteroot` we took the simplest possible step: a
root object with little need for the stitching-together of a tree known
as traversal.
In this step we remain simple, but make a basic hierarchy::
/
doc1
doc2
folder1/
doc1
Objectives
==========
- Multi-level nested hierarchy of Python objects
- Show how ``__name__`` and ``__parent__`` glue the hierarchy together
- Objects which last between requests
Steps
=====
#. We are going to use the previous step as our starting point:
.. code-block:: bash
(env27)$ cd ..; cp -r traversal_siteroot traversal_hierarchy; cd traversal_hierarchy
(env27)$ python setup.py develop
#. Provide a richer set of objects in
``traversal_hierarchy/tutorial/resources.py``:
.. literalinclude:: traversal_hierarchy/tutorial/resources.py
:linenos:
#. Have ``traversal_hierarchy/tutorial/views.py`` show information about
the resource tree:
.. literalinclude:: traversal_hierarchy/tutorial/views.py
:linenos:
#. Get ``traversal_hierarchy/tutorial/home.pt`` to display this richer
information:
.. literalinclude:: traversal_hierarchy/tutorial/home.pt
:language: html
:linenos:
#. Simplified tests in ``traversal_hierarchy/tutorial/tests.py``:
.. literalinclude:: traversal_hierarchy/tutorial/tests.py
:linenos:
#. Now run the tests:
.. code-block:: bash
(env27)$ nosetests tutorial
.
----------------------------------------------------------------------
Ran 4 tests in 0.141s
OK
#. Run your Pyramid application with:
.. code-block:: bash
(env27)$ pserve development.ini --reload
#. Open ``http://localhost:6543/`` in your browser.
Analysis
========
In this example we have to manage our tree by assigning ``__name__`` as
an identifier on each child and ``__parent__`` as a reference to the
parent.
The template used now shows different information based on the object
URL which you traversed to.
Extra Credit
============
#. In ``resources.py``, we moved the instantiation of ``root`` out to
global scope. Why?
#. If you go to a resource that doesn't exist, will Pyramid handle it
gracefully?
#. What happens if you use a ``__name__`` that already exists in the
container?
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