[Python-ideas] Bring line continuation to multi-level dictionary lookup

John Wong gokoproject at gmail.com
Thu Sep 17 06:07:50 CEST 2015

Hi everyone.

I work with APIs which have deep nested dictionary structure response.
Imagine a simplified case:

foo = {1: {2: {3: {4: {5: 6 } } } }

Now imagine I need to get to 6:


This looks managable, but if the key name is long, then I certainly will
end doing this to respect my style guide. To make it concrete, let's use
something reallistic, a response call from AWS API:

response = {'DescribeDBSnapshotsResponse': {'ResponseMetadata':
{'RequestId': '123456'}, 'DescribeDBSnapshotsResult': {'Marker': None,
'DBSnapshots': [{'Engine': 'postgres'}]}}}

If I had to get to the Engine I'd do this:

detail_response = response["DescribeDBSnapshotsResponse"]
result = detail_response["DescribeDBSnapshotsResult"]

This is only a few level deep, but imagine something slightly longer (I
strict out so much from this response). Obviously I am picking some real
example but key name being really long to sell my request.

Can we do it differently? How about

Okay. Not bad, almost like writing in Javascript except Python doesn't
allow you to do line continuation before the got at all, so you are stuck
with (.

But the problem with the alternative is that
if DescribeDBSnapshotsResult is a non-existent key, you will just get None,
because that's the beauty of the .get method for a dictionary object. So
while this allows you to write in slightly different way, I am costing
silent KeyError exception. I wouldn't know which key raised the exception.
Whereas with [key1][key2] I know if key1 doesn't exist, the exception will
explain to me that key1 does not exist.

So here I am, thinking, what if we can do this?


You get the point. This looks kinda ugly, but it doesn't require so many
assignment. I think this is doable, after all [ ] is still a method call
with the key name passed in. I am not familar with grammar, so I don't know
how hard and how much the implementation has to change to adopt this.

Let me know if this is a +1 or -10000000 bad crazy idea.


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