Use list items as keys for nested dictionary

Question

I want to use the items in a list as dictionary keys to find a value in nested dictionaries.

For example, given the following list:

keys = ['first', 'second', 'third']

I want to do:

result = dictionary[keys[0]][keys[1]][keys[2]]

Which would be the equivalent of:

result = dictionary['first']['second']['third']

But I don't know how many items will be in the keys list beforehand (except that it will always have at least 1).

have you tried addict.Dict - that's probably the easiest way. Otherwise of course you can iterate with .get() — user3467349
– user3467349, Commented Jan 28, 2015 at 18:46

maged · Accepted Answer · 2015-01-28 18:49:28Z

1

Iteratively go into the subdictionaries.

result = dictionary
for key in keys:
  result = result[key]
print(result)

answered Jan 28, 2015 at 18:49

maged

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Comments

user2555451 · Accepted Answer · 2015-01-28 18:49:04Z

0

A simple for-loop will work:

result = dictionary[keys[0]]  # Access the first level (which is always there)
for k in keys[1:]:            # Step down through any remaining levels
    result = result[k]

Demo:

>>> dictionary = {'first': {'second': {'third': 123}}}
>>> keys = ['first', 'second', 'third']
>>> result = dictionary[keys[0]]
>>> for k in keys[1:]:
...     result = result[k]
...
>>> result
123
>>>

answered Jan 28, 2015 at 18:49

user2555451

2 Comments

user3467349 Over a year ago

You should try, except or use get and break on None.

user2555451 Over a year ago

Why? keys is supposed to be a list of valid keys. If it contains one that does not exist, I would expect a KeyError to be raised. Suppressing this error would only lead to problems down the line.

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