python - Accessing values nested within dictionaries

Question

I have a dictionary which contains dictionaries, which may also contain dictionaries, e.g.

dictionary = {'ID': 0001, 'Name': 'made up name', 'Transactions':
               {'Transaction Ref': 'a1', 'Transaction Details':
                  {'Bill To': 'abc', 'Ship To': 'def', 'Product': 'Widget A'
                      ...} ...} ... }

Currently I'm unpacking to get the 'Bill To' for ID 001, 'Transaction Ref' a1 as follows:

if dictionary['ID'] == 001:
    transactions = dictionary['Transactions']
        if transactions['Transaction Ref'] == 'a1':
            transaction_details = transactions['Transaction Details']
            bill_to = transaction_details['Bill To']

I can't help but think this is is a little clunky, especially the last two lines - I feel like something along the lines of the following should work:

bill_to = transactions['Transaction Details']['Bill To']

Is there a simpler approach for drilling down into nested dictionaries without having to unpack into interim variables?

Answer 1

You can use something like this:

>>> def lookup(dic, key, *keys):
...     if keys:
...         return lookup(dic.get(key, {}), *keys)
...     return dic.get(key)
...
>>> d = {'a':{'b':{'c':5}}}
>>> print lookup(d, 'a', 'b', 'c')
5
>>> print lookup(d, 'a', 'c')
None

Additionally, if you don't want to define your search keys as individual parameters, you can just pass them in as a list like this:

>>> print lookup(d, *['a', 'b', 'c'])
5
>>> print lookup(d, *['a', 'c'])
None