How to call get() on dictionary with indexes?

Question

I have an array of dictionaries but i am running into a scenario where I have to get the value from 1st index of the array of dictionaries, following is the chunk that I am trying to query.

address_data = record.get('Rdata')[0].get('Adata')

This throws the following error:

TypeError: 'NoneType' object is not subscriptable

I tried following:

if record.get('Rdata') and record.get('Rdata')[0].get('Adata'):
   address_data = record.get('Rdata')[0].get('Adata')

but I don't know if the above approach is good or not.

So how to handle this in python?

Edit:

"partyrecord": {

      "Rdata": [
        {

          "Adata": [
            {
              "partyaddressid": 172,
              "addressid": 142165
            }
          ]

        }
      ]
    }

This may help: https://stackoverflow.com/questions/31033549/nested-dictionary-value-from-key-path — rdas, Apr 04 '19 at 19:04
You can one-line this: `address_data = bool(record.get('Rdata')) and record.get('Rdata')[0].get('Adata') or None` - you can replace `None` with whatever fallback value you want — JacobIRR, Apr 04 '19 at 19:05
@JacobIRR `len(record.get('Rdata'))` immediately fails if the value doesn't exist because it becomes `len(None)` — roganjosh, Apr 04 '19 at 19:06
`record.get('Rdata')` this is returning `None`. You need to break up this statement to handle that case — Paul H, Apr 04 '19 at 19:07
@JacobIRR Wouldn't that just return 1 or 0 and not the actual value inside the dict? — alex067, Apr 04 '19 at 19:07
@JacobIRR you've fixed the error, but no need for `bool` now :) `None` is falsey, so just `if record.get('Rdata') and...` but even then, you can return an empty dict if the first lookup fails — roganjosh, Apr 04 '19 at 19:09
I see the example but it's disembodied from the problem you describe. There is no `Rdata` key. Please give a [mcve]. The level of nesting for `record` is too deep for your approach to work with that sample. — roganjosh, Apr 04 '19 at 19:10
@noobie-php, your proposed solution seems ok to me. It avoids the issue mentioned in the comments because `if record.get('Rdata')` checks both for the record 'Rdata' to exist in 'record', and for it to reference a container that has something in it. So you should safely be able to say `record.get('Rdata')[0]` if this test succeeds. (assuming your assumptions about your data are otherwise correct). — CryptoFool, Apr 04 '19 at 19:10
@noobie-php, ...now, about your data...first of all, I assume you want a pair of curly braces around what you've given us, as what you have here isn't legal Python by itself. what do you want to do exactly with this data? — CryptoFool, Apr 04 '19 at 19:12

chepner · Answer 1 · 2019-04-04T19:22:02.427

Your expression assumes that record['Rdata'] will return a list with at least one element, so provide one if that isn't the case.

address_data = record.get('Rdata', [{}])[0].get('Adata')

Now if record['Rdata'] doesn't exist, you'll still have an empty dict on which to invoke get('Adata'). The end result will be address_data being set to None.

(Checking for the key first is preferable if a suitable default is expensive to create, since it will be created whether get needs to return it or not. But [{}] is fairly lightweight, and the compiler can generate it immediately.)

score 3 · Answer 2 · answered Apr 04 '19 at 19:13

3

You might want to go for the simple, not exciting route:

role_data = record.get('Rdata')

if role_data:
  address_data = role_data[0].get('Adata')
else:
  address_data = None

answered Apr 04 '19 at 19:13

Aviv Goldgeier

799
7
23

This fails if there is role_data but it isn't an iterable. I guess we can assume it will be – amchugh89 Apr 04 '19 at 19:16
1

It may be OK to assume that `record` is well-formed, but that `Rdata` is simply optional, rather than accommodating every possible `dict`. (We're also assuming that `record` has a `get` method in the first place.) – chepner Apr 04 '19 at 19:18

How to call get() on dictionary with indexes?

2 Answers2