如何在带有索引的字典上调用get（）？

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
            }
          ]

        }
      ]
    }

Answer 1

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.)

Answer 2

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