вы можете использовать:
from itertools import chain
r = {"response" :[{"sent":46},{"drafts":2},{"completed":48},{"pending":1}]}
r['response'] = dict(chain(*map(dict.items, r['response'])))
# same with:
# r['response'] = dict(chain.from_iterable(map(dict.items, r['response'])))
r
вывод:
{'response': {'sent': 46, 'drafts': 2, 'completed': 48, 'pending': 1}}
или вы можете использовать словарь понимания:
r['response'] = {k: v for d in r['response'] for k, v in d.items()}
вывод:
{'response': {'sent': 46, 'drafts': 2, 'completed': 48, 'pending': 1}}