import re
pattern =r"(?<!\d,)(?<!\d)[1-9][0-9]{0,2}(?:,\d{3})*(?!,?\d)"
string = '42 1,234 6,368,745 12,34,567 1234'
a = re.findall(pattern,string)
print(a)
aW1wb3J0IHJlCnBhdHRlcm4gPXIiKD88IVxkLCkoPzwhXGQpWzEtOV1bMC05XXswLDJ9KD86LFxkezN9KSooPyEsP1xkKSIKc3RyaW5nID0gJzQyIDEsMjM0IDYsMzY4LDc0NSAxMiwzNCw1NjcgMTIzNCcKYSA9IHJlLmZpbmRhbGwocGF0dGVybixzdHJpbmcpCnByaW50KGEp