import re
r = r'{([\w\s,]+)}'
s = "{Cat}\n{Cow Pig}\n{Cat,Dog}\ncat dog fish"
print( re.sub(r, lambda x: "{{{}}}".format(re.sub(r'\w+', r'"\g<0>"', x.group(1))), s) )
aW1wb3J0IHJlCnIgPSByJ3soW1x3XHMsXSspfScKcyA9ICJ7Q2F0fVxue0NvdyBQaWd9XG57Q2F0LERvZ31cbmNhdCBkb2cgZmlzaCIKcHJpbnQoIHJlLnN1YihyLCBsYW1iZGEgeDogInt7e319fSIuZm9ybWF0KHJlLnN1YihyJ1x3KycsIHInIlxnPDA+IicsIHguZ3JvdXAoMSkpKSwgcykgKQ==