convert a list of delimited strings to a tree/nested dict, using python

Question

I am trying to convert a list of dot-separated strings, e.g.

['one.two.three.four', 'one.six.seven.eight', 'five.nine.ten', 'twelve.zero']

into a tree (nested lists or dicts - anything that is easy to walk through). The real data happens to have 1 to 4 dot-separated parts of different length and has 2200 records in total. My actual goal is to fill in the set of 4 QComboBox'es with this data, in manner that the 1st QComboBox is filled with first set items ['one', 'five', 'twelve'] (no duplicates). Then depending on the chosen item, the 2nd QComboBox is filled with its related items: for 'one' it would be: ['two', 'six'], and so on, if there's another nested level.

So far I've got a working list -> nested dicts solution, but it's horribly slow, since I use regular dict(). And I seem to have a trouble to redesign it to a defaultdict in a way to easily work out filling the ComboBoxes properly.

My current code:

def list2tree(m):
    tmp = {}
    for i in range(len(m)):
        if m.count('.') == 0:
            return m
        a = m.split('.', 1)
        try:
            tmp[a[0]].append(list2tree(a[1]))
        except (KeyError, AttributeError):
            tmp[a[0]] = list2tree(a[1])
    return tmp

main_dict = {}
i = 0
for m in methods:
    main_dict = list2tree(m)
    i += 1
    if (i % 100) == 0: print i, len(methods)
print main_dict, i, len(methods)

Answer 1

ls = ['one.two.three.four', 'one.six.seven.eight', 'five.nine.ten', 'twelve.zero']
tree = {}

for item in ls:
    t = tree
    for part in item.split('.'):
        t = t.setdefault(part, {})

Result:

{
 "twelve": {
  "zero": {}
 }, 
 "five": {
  "nine": {
   "ten": {}
  }
 }, 
 "one": {
  "six": {
   "seven": {
    "eight": {}
   }
  }, 
  "two": {
   "three": {
    "four": {}
   }
  }
 }
}