Convenient way to handle deeply nested dictionary in Python

Question

I have a deeply nested dictionary in python thats taking up a lot of room. Is there a way to abbreviate something like this

master_dictionary['sub_categories'][sub_cat_name]['attributes'][attribute_name]['special_type']['nested_children'][child_cat_name][color] = blue

to this for example

nested_child_info[color] = blue

And still have it edit the dictionary ? I hope that makes sense.

Answer 1

Similar to @fferri. You will always have to specify the items in a long list. Get a reference to the final dict using reduce and getitem:

from functools import reduce
from operator import getitem

d = {1:{2:{3:{4:5}}}}

foo = 2
items = [1,foo,3]
result = d
info = reduce(getitem, items, d)


>>> info[4]
5
>>> d
{1: {2: {3: {4: 5}}}}
>>> info[4] = 99
>>> d
{1: {2: {3: {4: 99}}}}

---

I was also playing around with a class but it doesn't seem to have many advantages - except you could customize a key error exception so that the error message would tell you which key at which depth is missing.

class Drilldown:
    def __init__(self, d, path):
        #self.final = reduce(getitem, path, d)
        self.final = d
        for i, item in enumerate(path, 1):
            try:
                self.final = self.final[item]
            except KeyError as e:
                msg = ''.join('[{}]' for _ in range(i))
                msg = msg.format(*path[:i])
                msg = 'The last key in the path "{}" does not exist'.format(msg)
                e.args = [msg]
                raise
    def __call__(self, item):
        return self.final[item]
    def __setitem__(self, item, value):
        self.final[item] = value
    def __getitem__(self, item):
        return self.final[item]
    def __str__(self):
        return str(self.final)
    def __repr__(self):
        return repr(self.final)

>>> z = 19
>>> items = [1,2,z]
>>> q = Drilldown(d,items)
Traceback (most recent call last):
  File "<pyshell#68>", line 1, in <module>
    q = Drilldown(d,items)
  File "C:\pyProjects33\tmp.py", line 32, in __init__
    self.final = self.final[item]
KeyError: 'The last key in the path "[1][2][19]" does not exist'

>>> 
>>> #normal usage
>>> items = [1,2,3]
>>> q = Drilldown(d,items)
>>> d
{1: {2: {3: {4: 5}}}}
>>> q
{4: 5}
>>> q(4)
5
>>> q[4]
5
>>> q[4] += 20
>>> q
{4: 25}
>>> d
{1: {2: {3: {4: 25}}}}
>>> q['foo'] = '99'
>>> q
{4: 25, 'foo': '99'}
>>> d
{1: {2: {3: {4: 25, 'foo': '99'}}}}
>>>