Tree structure

[Bevan Jenkins]

Hello,

I am trying to create a tree structure for use with a PyQt QTreeView.
But first I need to get my head around how to create the tree
structure.  I have a dictionary (for testing purposes) but I will
later use a table via sqlalchemy.

The use case is hydrology, so I  would like to have a hydrologically
connected river tree, in which you can browse upstream from the sea
(making choices) or downstream from any named hydrological feature.
Each key flows into its value pair. myrivers =
{"river":"flows_into"}.  An example is below:

myrivers = {"little stream":"sea",
    "mountain stream":"lake",
    "lake":"big river",
    "cold spring":"big river",
    "big river":"sea"
    "sea":""}

I would like the tree to look like (if the formatting works....). so
you can browse downstream from each named river but also upstream from
the sea picking which direction to go.

little stream
    sea
mountain stream
    lake
        big river
            sea
lake
    big river
        sea
cold spring
    big river
        sea
big river
    sea
sea
    little stream
    big river
        lake
            mountain stream
        cold spring

<<this next part is probably not very clear>>
So every key is a parent.  For all keys that have a value (not ""),
the value is the child and is then used as a parent to get the next
child until the sea and a value of "" is reached.  For the sea this is
reversed, that you find all rivers that flow into the sea and then all
rivers that flow into them.


Any thoughts about how to acomplish this will be much appreciated,
Bevan