is_valid_email_address.py

"""
Implements an is valid email address algorithm

@ https://en.wikipedia.org/wiki/Email_address
"""

importstring

email_tests: tuple[tuple[str, bool], ...] = (
 ("simple@example.com", True),
 ("very.common@example.com", True),
 ("disposable.style.email.with+symbol@example.com", True),
 ("other-email-with-hyphen@and.subdomains.example.com", True),
 ("fully-qualified-domain@example.com", True),
 ("user.name+tag+sorting@example.com", True),
 ("x@example.com", True),
 ("example-indeed@strange-example.com", True),
 ("test/test@test.com", True),
 (
"123456789012345678901234567890123456789012345678901234567890123@example.com",
True,
 ),
 ("admin@mailserver1", True),
 ("example@s.example", True),
 ("Abc.example.com", False),
 ("A@b@c@example.com", False),
 ("abc@example..com", False),
 ("a(c)d,e:f;g<h>i[j\\k]l@example.com", False),
 (
"12345678901234567890123456789012345678901234567890123456789012345@example.com",
False,
 ),
 ("i.like.underscores@but_its_not_allowed_in_this_part", False),
 ("", False),
)

# The maximum octets (one character as a standard unicode character is one byte)
# that the local part and the domain part can have
MAX_LOCAL_PART_OCTETS=64
MAX_DOMAIN_OCTETS=255


defis_valid_email_address(email: str) ->bool:
"""
 Returns True if the passed email address is valid.

 The local part of the email precedes the singular @ symbol and
 is associated with a display-name. For example, "john.smith"
 The domain is stricter than the local part and follows the @ symbol.

 Global email checks:
 1. There can only be one @ symbol in the email address. Technically if the
 @ symbol is quoted in the local-part, then it is valid, however this
 implementation ignores "" for now.
 (See https://en.wikipedia.org/wiki/Email_address#:~:text=If%20quoted,)
 2. The local-part and the domain are limited to a certain number of octets. With
 unicode storing a single character in one byte, each octet is equivalent to
 a character. Hence, we can just check the length of the string.
 Checks for the local-part:
 3. The local-part may contain: upper and lowercase latin letters, digits 0 to 9,
 and printable characters (!#$%&'*+-/=?^_`{|}~)
 4. The local-part may also contain a "." in any place that is not the first or
 last character, and may not have more than one "." consecutively.

 Checks for the domain:
 5. The domain may contain: upper and lowercase latin letters and digits 0 to 9
 6. Hyphen "-", provided that it is not the first or last character
 7. The domain may also contain a "." in any place that is not the first or
 last character, and may not have more than one "." consecutively.

 >>> for email, valid in email_tests:
 ... assert is_valid_email_address(email) == valid
 """

# (1.) Make sure that there is only one @ symbol in the email address
ifemail.count("@") !=1:
returnFalse

local_part, domain=email.split("@")
# (2.) Check octet length of the local part and domain
iflen(local_part) >MAX_LOCAL_PART_OCTETSorlen(domain) >MAX_DOMAIN_OCTETS:
returnFalse

# (3.) Validate the characters in the local-part
ifany(
charnotinstring.ascii_letters+string.digits+".(!#$%&'*+-/=?^_`{|}~)"
forcharinlocal_part
 ):
returnFalse

# (4.) Validate the placement of "." characters in the local-part
iflocal_part.startswith(".") orlocal_part.endswith(".") or".."inlocal_part:
returnFalse

# (5.) Validate the characters in the domain
ifany(charnotinstring.ascii_letters+string.digits+".-"forcharindomain):
returnFalse

# (6.) Validate the placement of "-" characters
ifdomain.startswith("-") ordomain.endswith("."):
returnFalse

# (7.) Validate the placement of "." characters
returnnot (domain.startswith(".") ordomain.endswith(".") or".."indomain)


if__name__=="__main__":
importdoctest

doctest.testmod()

foremail, validinemail_tests:
is_valid=is_valid_email_address(email)
assertis_valid==valid, f"{email} is {is_valid}"
print(f"Email address {email} is {'not 'ifnotis_validelse''}valid")