Convert dictionary 'key' in list to lowercase (python3)

Using List Comprehension and Dictionary Comprehension
>>> rs = [{'ABC': '123', 'DEF': '456'}]
>>> ret = [{k.lower():v for k,v in i.items()} for i in rs]
>>> ret
>>> [{'abc': '123', 'def': '456'}]

Using Lambda Function
>>> rs = list(map((lambda i: { k.lower(): v for k,v in i.items()}), rs))