I did some searching to see if this has already been proposed before, but 
didn't find any evidence that it has.  If so, let me know and I'll go away :)

One of the tasks that I encounter frequently enough is retrieving a nested key 
from a nested collection of dictionaries (a dictionary of dictionaries that can 
be any number of layers deep).  There are multiple ways of tackling this, 
normally done with `reduce()`, iterative looping or chained `get()`s and then 
handling `None`, `KeyError` or `AttributeError` appropriately.  I'd like to 
avoid this extra code and logic and have a built-in method to facilitate this 
common data access pattern.

I'd like to propose that we add a `dig()` method to dictionaries analogous to 
Ruby's `dig()` method for Ruby Hashes (reference: 
https://ruby-doc.org/core-2.6.0.preview2/Hash.html#method-i-dig).  Initially, 
I'd suggest that we only support nested dictionaries, but we could also support 
lists and other collection types as Ruby does if we really want to.  Similar to 
the existing `get()` method on dictionaries, I'd propose that the method return 
`None` if any of the keys in the chain is not found, avoiding `KeyError`.

Thoughts?
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