Thanks to Matthew and Denis for trying to enlighten me. Thanks to your
clues I've made some progress; however, I can't seem to get the hang of
the usual recursion trick of keeping track of the level one is on. It
doesn't work, I suppose, because the data structure I'm traversing isn't
actually nested, its a flat series of lists of tuples.
I did finally get a function to traverse the "tree-like" data coming from
the db
getRecord() returns a tuple of record-type, record-id, parent-id, and
title, thus:
('work', 47302, 47301, 'record title')
getImages(id) returns a list of 'image' tuples whose parent-id is id
getWorks(id) returns a list of 'work' tuples whose parent-id is id
works can be nodes, images can't
so:
def makeDecendentList(id, result):
result.append(getRecord(id))
if getImages(id):
for x in getImages(id):
result.append(x)
if not getWorks(id):
return
else:
for y in getWorks(id):
makeDecendentList(y[1],result)
return result
called with the empty list as the second argument.
Well and good. This walks the 'tree' (following the parent-ids) and
returns me a list of all the decendents of id. But what I wanted was a
nested data structure.
In the fashion of an ape given a typewriter and sufficient time, I trial
and errored my way to this:
def makeNestedLists(id):
result = []
result.append(getRecord(id))
result.extend(getImages(id))
if not getWorks(id):
return result
else:
result.extend([makeNestedLists(x[1]) for x in getWorks(id)])
return result
To my surprise, this gets me exactly what I wanted, eg:
[ ('work', 47301, 47254, 'a title'),
('image', 36871, 47301, 'a title'),
('image', 36872, 47301, 'a title'),
[ ('work', 47302, 47301, 'a title'),
('image', 10706, 47302, 'a title'),
('image', 10725, 47302, 'a title')
]
]
To my surprise, I say, because it looks like it shouldn't work at all with
the result being set to the empty list with each recursion; moreover, if I
spell out the loop in the list comp like this:
def makeNestedLists(id):
result = []
result.append(getRecord(id))
result.extend(getImages(id))
if not getWorks(id):
return result
else:
for x in getWorks(id):
result.extend(makeNestedLists(x[1]))
return result
I once again get a flat list of all the decendents of id.
I know it's sad, but can any wise tutor explain to me what's going on in
the code that I myself wrote?
Thanks,
Jon
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