creating nested dictionaries in python from database query

Question

I have information I'm retrieving from a database:

with fields like

and data like

("us", "2013-01", "Consumer","Retail","PM",10,1000)
("us", "2013-01", "Consumer", "Retail", "JCP", 15, 1500) ...

How can I turn this into a dictionary that looks like:

{us:{"2013-01":{"Consumer":{"Retail":{"PM":{"Price":10,"Position":1000},"JCP":{"Price":15, "Position":1500}}}}}}

in the most time and resource effective way?

something like

a[Date][Sector][Industry][Ticker].update("PM2" = dict(close=10, position = 1000))

gives me an error.

Thanks

Dont do this {us:{"2013-01":{"Consumer":{"Retail":{"PM":{"Price":10,"Position":1000},"JCP":{"Price":15, "Position":1500}}}}}} its not how dictionaries are meant to be used. Instead put all the key:value pairs in one {} bracket pair — Tim
– Tim, Commented Nov 19, 2014 at 14:21
I agree with @TimCastelijns, your example looks ugly, you should probably rethink your decision to use it like that. — Rusty
– Rusty, Commented Nov 19, 2014 at 14:23
Hi @TimCastelijns. Thanks for the comments. The reason I'm going with this approach is that in the final program I'll have multiple dates and I'll need to run calculations for each industry for each day. Some of those calculations will require aggregated numbers from each industry. I thought having hash key lookups would give me a performance advantage over multiple nested loops or filter requests. Is that incorrect? — Tahnoon Pasha
– Tahnoon Pasha, Commented Nov 20, 2014 at 1:37
Unless it makes your program run real slow, pick readability over performance. You know what you need best, though — Tim
– Tim, Commented Nov 20, 2014 at 7:57

iamkhush · Accepted Answer · 2014-11-19 14:26:38Z

1

You havent specified what error.

Anyways, this can be done by iterating each row and using the setdefault method dict, where you can check item and see if its already present in the dict.

So, for example -

a = {}
a.setdefault('us', {})
....
....
# if a now is 
# {'us':{"2013-01":{"Consumer":{"Retail":{"PM":{"Price":10,"Position":1000}}}}}}
# and you are iterating on 2nd row
a['us']['2013-01']['Consumer']['Retail'].setupdate('JCP', {})
.....

You may want to write a function for that. This is just an idea on how a better approach can be written.

answered Nov 19, 2014 at 14:26

iamkhush

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