CODEWITHSUNDEEP
pythonpython-2.7dictionary-comprehension
2rs2ts
2rs2ts

Reputation: 11066

*Very* nested dict comprehension from tuples

I have data like so (yes, these tuples are guaranteed to have exactly 5 elements):

ts = ([('a','b','c','d','e'), ('v','w','x','y','z'),
       ('f','g','h','i','j'), ('a','foo','bar',1,2),
       ('f','g','baz',1,3), ('f','g','baz',3,4)])

I'm trying to parse it into a nested dictionary structure like so:

d = {
    'a': {
        'b': {
            'c': [('d','e')]
        },
        'foo': {
            'bar': [(1,2)]
        }
    },
    'f': {
        'g': {
            'h': [('i', 'j')],
            'baz': [(1,3), (3,4)]
        }
    },
    'v': {
        'w': {
            'x': [('y', 'z')]
        }
    }
}

Here's what I have so far; it seems to work properly:

>>> d = {}
>>> for t in ts:
...     if t[0] not in d:
...         d[t[0]] = {t[1]: {t[2]: [(t[3], t[4])]}}
...     elif t[1] not in d[t[0]]:
...         d[t[0]][t[1]] = {t[2]: [(t[3], t[4])]}
...     elif t[2] not in d[t[0]][t[1]]:
...         d[t[0]][t[1]][t[2]] = [(t[3], t[4])]
...     else:
...         d[t[0]][t[1]][t[2]].append((t[3],t[4]))
... 
>>> d
{'a': {'b': {'c': [('d', 'e')]}, 'foo': {'bar': [(1, 2)]}}, 'f': {'g': {'h': [('i', 'j')], 'baz': [(1, 3), (3, 4)]}}, 'v': {'w': {'x': [('y', 'z')]}}}

When I attempted this comprehension, of course, some of the values got overwritten:

>>> {t[0]: {t[1]: {t[2]: [(t[3],t[4])]}} for t in ts}
{'a': {'foo': {'bar': [(1, 2)]}}, 'f': {'g': {'baz': [(3, 4)]}}, 'v': {'w': {'x': [('y', 'z')]}}}

And you really don't want to see the result of this:

>>> {t[0]: {t[1]: {t[2]: [(t[3],t[4])] for t in ts} for t in ts} for t in ts}

How do I correctly write this dict comprehension?

Edit: I'm sorry, I forgot to mention - I need this to be a regular dictionary at the end of the day (it's getting converted to an NSDictionary via PyObjC eventually).

Upvotes: 0

Views: 164

Answers (1)

Blckknght
Blckknght

Reputation: 104762

I'd set up the dictionary automatically built its own nested structure as needed:

from collections import defaultdict

dct = defaultdict(lambda: defaultdict(lambda: defaultdict(list)))

Then just append the 2-tuples into the right list:

for a, b, c, d, e in ts:
    dct[a][b][c].append((d, e))

If the different levels of indexing have meanings, I'd use better names than a, b, c though.

Upvotes: 5

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