import re
p = re.compile(r'[\w.-]+@(?![\w.-]*\.(?:png|jpe?g|gif)\b)[\w.-]+\b')
test_str = "{'email': ['billy666@stanford.edu',\n 'cantorfamilies@stanford.edu',\n 'cantorfamilies@stanford.edu',\n 'cantorfamilies@stanford.edu',\n 'footer-stanford-logo@2x.png']}"
print(set(p.findall(test_str)))
aW1wb3J0IHJlCnAgPSByZS5jb21waWxlKHInW1x3Li1dK0AoPyFbXHcuLV0qXC4oPzpwbmd8anBlP2d8Z2lmKVxiKVtcdy4tXStcYicpCnRlc3Rfc3RyID0gInsnZW1haWwnOiBbJ2JpbGx5NjY2QHN0YW5mb3JkLmVkdScsXG4gICAgICAgICAgICdjYW50b3JmYW1pbGllc0BzdGFuZm9yZC5lZHUnLFxuICAgICAgICAgICAnY2FudG9yZmFtaWxpZXNAc3RhbmZvcmQuZWR1JyxcbiAgICAgICAgICAgJ2NhbnRvcmZhbWlsaWVzQHN0YW5mb3JkLmVkdScsXG4gICAgICAgICAgICdmb290ZXItc3RhbmZvcmQtbG9nb0AyeC5wbmcnXX0iCnByaW50KHNldChwLmZpbmRhbGwodGVzdF9zdHIpKSk=