Every string is changing to NaN while assigning a Key value pair in Dict

data_utterance = pd.read_csv("Ruby_test/utterance.csv")
data_responses = pd.read_csv("Ruby_test/responses.csv")
r,c = data_utterance.shape
r1,c1 = data_responses.shape

s_out = defaultdict(dict)

for i in range(0,r):
  s_out.setdefault(data_utterance.iloc[i,0],[]).append({'query': data_utterance.iloc[i,1]})
#print(s_out)


out = defaultdict(dict)
for i in intent:
  for j in locales:
    out[i][j] = s_out[i]

for i in range(0,r1):
  for j in range(0,len(out[data_responses.iloc[i,0]][data_responses.iloc[i,1]])):
    out[data_responses.iloc[i,0]][data_responses.iloc[i,1]][j]['response']=data_responses.iloc[i,2]
result = json.dumps(out, indent = 4)
print(result)

When i print the result, every value tagged to key 'response' is updated as NaN.

Data responses contain both NaN and Strings.