Is it possible to catch empty nested attributes in python?

Question

I'm trying to create a custom object that supports nested attributes.

I need to implement a specific kind of search.

If an attribute doesn't exist at the lowest level, I want to recurse and see if the attribute exists at a higher level.

I've spent all day trying to do this. The closest I've come is being able to print the attribute search path.

class MyDict(dict):
  def __init__(self):
    super(MyDict, self).__init__()

  def __getattr__(self, name):
    return self.__getitem__(name)

  def __getitem__(self, name):
    if name not in self:
      print name
      self[name] = MyDict()
    return super(MyDict, self).__getitem__(name)

config = MyDict()
config.important_key = 'important_value'
print 'important key is: ', config.important_key
print config.random.path.to.important_key

Output:

important key is:  important_value
random
path
to
important_key
{}

What I need to happen is instead to see if important_key exists at the lowest level ( config.random.path.to ), then go up a level ( config.random.path ) and only return None if it doesn't exist at the top level.

Do you think this is possible?

Thank you so much!

Answer 1

Yes, it's possible. In your search routine, recur to the end of the path, checking for the desired attribute. At the bottom level, return the attribute if found, None otherwise. At each non-terminal level, recur to the next level down.

if end of path   # base case
    if attribute exists here
        return attribute
    else
        return None
else  # some upper level
    exists_lower = search(next level down)
    if exists_lower
        return exists_lower
    else
        if attribute exists here
            return attribute
        else
            return None

Does this pseudo code get you moving toward a solution?