I see a lot of complicated answers here. Some of them, fail to knowledge simple, true email address, or have false positives. Below, is the simplest way of testing that the string would be a valid email. It tests against 2 and 3 letter TLD's. Now that you technically can have larger ones, you may wish to increase the 3 to 4, 5 or even 10.
import re
def valid_email(email):
return bool(re.search(r"^[\w\.\+\-]+\@[\w]+\.[a-z]{2,3}$", email))