import re
s = ' {"start": 2542, "end": 2546, "text": "Asia", "labels": ["LOC"]}]'
m = re.search(r'"labels": \["([^][]*)\"]', s)
if m:
print(m.group(1))
aW1wb3J0IHJlCnMgPSAnIHsic3RhcnQiOiAyNTQyLCAiZW5kIjogMjU0NiwgInRleHQiOiAiQXNpYSIsICJsYWJlbHMiOiBbIkxPQyJdfV0nCm0gPSByZS5zZWFyY2gocicibGFiZWxzIjogXFsiKFteXVtdKilcIl0nLCBzKQppZiBtOgoJcHJpbnQobS5ncm91cCgxKSk=