Processing data from GraphQL to CSV. Install the ijson module first.

data-from-graphql.py

#!/usr/bin/env python3

import csv, ijson, sys

items = ijson.items(sys.stdin, "data.documentaryUnits.items.item")
csvout = csv.writer(sys.stdout, quoting = csv.QUOTE_MINIMAL)

for item in items:
    for description in item["descriptions"]:
        row = [ 
                description["scopeAndContent"],
                description["biographicalHistory"],
                description["systemOfArrangement"]]
        if [r for r in row if r is not None]:
            csvout.writerow([item["id"]] + row) 

query.gql

query documentaryUnitData {
  documentaryUnits {
    items {
      id
      descriptions {
        languageCode
        biographicalHistory
        scopeAndContent
        systemOfArrangement
      }
    }
  }
}