将JSON字段复制到另一个JSON结构的最pythonic方法是什么？

Question

Here's the context:

• I have a database that cannot accept partial updates of its JSON structures. To modify a record you must read the whole JSON record, make modifications and then write back the JSON record, overwriting the previous JSON record.

• We receive updates from end users to these JSON records. We do not blindly trust that the user is providing a valid and complete new JSON record, so we check that their update contains only field-names that we permit.

So, the objective is to say something like:

1: receive inbound JSON from user along with record id
2: grab the existing JSON from the database for that record id
3: for each fieldname in (a list of permitted fieldnames)
  4: if the fieldname is present in the inbound JSON
      5: add that field or update its contents to the existing JSON record
6: write the resulting JSON structure back to the database

My question is, what is the most Pythonic way to implement steps 3, 4 and 5?

I know Python is extremely good at such things and I have seen some very elegant code that does similar things.

Can anyone suggest a general approach that is very elegant and Pythonic?

Please note I'm only interested in Python 3.

thanks

Answer 1

existing = {"a": 1, "b": 2, "c": 3}
inbound = {"b": 3, "c": 4, "d": 5}
permitted = {"a","b","c"}
existing.update((key, val) for (key, val) in inbound.items() if key in permitted)