import re
regex = re.compile(r"(?P<username>[a-zA-Z0-9.-_]+)@(?P<domain>[a-zA-Z0-9.-_]+)\.(?P<ltd>[a-zA-Z0-9-_]+)", flags=re.MULTILINE)
test_str = ("The mail or post is a system for physically transporting postcards, letters, and parcels.[1] A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century,yvannak54@gmail.com national postal systems have generally been established as a government monopoly, with a fee on the article prepaid. Proof of payment is usually in the form of an adhesive postage stamp, but a it123@gmail.com postage meter is also used for bulk mailing. Modern private postal systems are distinguished from national postal agencies by the terms \"courier\" or \"delivery service\".\n")
subst = "<a href=\"mailto:\\0\">${username}</a>"
result = regex.sub(subst, test_str)
if result:
print(result)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Python, please visit: https://docs.python.org/3/library/re.html