Tres Traversal placeholder example

traversal.py

"""
On 01/30/2011 09:04 AM, Wade Leftwich wrote:
If you want to stick with Traversal, don't forget that you have
request.subpath available to you. For the path "/blog/archive/
2011/01/29/my-post-about-pyramid", you could have an Archive context
whose default (unnamed) view  would be called with a request that
included request.subpath = ['2011', '01', '29', 'my-post-about-
pyramid'].

Other traversal-based strategies:

- - an 'archive' view registered for  the blog context (assuming you don't
 otherwise need the 'archive' context).

- - add non-persistent placeholder objects to your app to take advantage
 of traversal's use of '__getitem__'.  This solution allows you write
 views for the "transient" context classes, even though they aren't in
 your database.  E.g., something like:
"""

class Blog:
   ...
   def __getitem__(self, key):
       if key == 'archive':
           return Archive(self)
       return super(Blog, self).__getitem__(key)

class Archive:
   __name__ = 'archive'
   YEARS = range(2010, 2100)
   def __init__(self, blog):
       self.__parent__ = self.blog = blog
   def __getitem__(self, key):
       try:
           year = int(key)
       except TypeError:
           raise KeyError(key)
       if year not in self.YEARS:
           raise KyeError(key)
       return ArchiveYear(self, year)

class ArchiveYear:
   __name__ = 'archive'
   MONTHS = range(1, 12)
   def __init__(self, archive, year):
       self.__parent__ = archive
       self.__name__ = str(year)
       self.blog = archive.blog
       self.year = year
   def __getitem__(self, key):
       try:
           mnnth = int(key)
       except TypeError:
           raise KeyError(key)
           # or, return self.blog.entries[key]
       if month not in self.MONTHS:
           raise KeyError(key)
       return ArchiveMonth(self, month)

class ArchiveMonth:
   __name__ = 'archive'
   MONTHS = range(1, 12)
   def __init__(self, year, month):
       self.__parent__ = year
       self.__name__ = str(month)
       self.blog = year.blog
       self.month = month
   def __getitem__(self, key):
       return self.blog.entries[key]