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116 lines
4.3 KiB
Python
116 lines
4.3 KiB
Python
"""
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Implements an is valid email address algorithm
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@ https://en.wikipedia.org/wiki/Email_address
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"""
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import string
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email_tests: tuple[tuple[str, bool], ...] = (
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("simple@example.com", True),
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("very.common@example.com", True),
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("disposable.style.email.with+symbol@example.com", True),
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("other-email-with-hyphen@and.subdomains.example.com", True),
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("fully-qualified-domain@example.com", True),
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("user.name+tag+sorting@example.com", True),
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("x@example.com", True),
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("example-indeed@strange-example.com", True),
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("test/test@test.com", True),
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(
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"123456789012345678901234567890123456789012345678901234567890123@example.com",
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True,
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),
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("admin@mailserver1", True),
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("example@s.example", True),
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("Abc.example.com", False),
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("A@b@c@example.com", False),
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("abc@example..com", False),
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("a(c)d,e:f;g<h>i[j\\k]l@example.com", False),
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(
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"12345678901234567890123456789012345678901234567890123456789012345@example.com",
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False,
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),
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("i.like.underscores@but_its_not_allowed_in_this_part", False),
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("", False),
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)
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# The maximum octets (one character as a standard unicode character is one byte)
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# that the local part and the domain part can have
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MAX_LOCAL_PART_OCTETS = 64
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MAX_DOMAIN_OCTETS = 255
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def is_valid_email_address(email: str) -> bool:
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"""
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Returns True if the passed email address is valid.
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The local part of the email precedes the singular @ symbol and
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is associated with a display-name. For example, "john.smith"
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The domain is stricter than the local part and follows the @ symbol.
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Global email checks:
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1. There can only be one @ symbol in the email address. Technically if the
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@ symbol is quoted in the local-part, then it is valid, however this
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implementation ignores "" for now.
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(See https://en.wikipedia.org/wiki/Email_address#:~:text=If%20quoted,)
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2. The local-part and the domain are limited to a certain number of octets. With
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unicode storing a single character in one byte, each octet is equivalent to
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a character. Hence, we can just check the length of the string.
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Checks for the local-part:
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3. The local-part may contain: upper and lowercase latin letters, digits 0 to 9,
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and printable characters (!#$%&'*+-/=?^_`{|}~)
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4. The local-part may also contain a "." in any place that is not the first or
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last character, and may not have more than one "." consecutively.
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Checks for the domain:
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5. The domain may contain: upper and lowercase latin letters and digits 0 to 9
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6. Hyphen "-", provided that it is not the first or last character
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7. The domain may also contain a "." in any place that is not the first or
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last character, and may not have more than one "." consecutively.
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>>> for email, valid in email_tests:
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... assert is_valid_email_address(email) == valid
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"""
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# (1.) Make sure that there is only one @ symbol in the email address
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if email.count("@") != 1:
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return False
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local_part, domain = email.split("@")
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# (2.) Check octet length of the local part and domain
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if len(local_part) > MAX_LOCAL_PART_OCTETS or len(domain) > MAX_DOMAIN_OCTETS:
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return False
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# (3.) Validate the characters in the local-part
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if any(
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char not in string.ascii_letters + string.digits + ".(!#$%&'*+-/=?^_`{|}~)"
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for char in local_part
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):
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return False
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# (4.) Validate the placement of "." characters in the local-part
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if local_part.startswith(".") or local_part.endswith(".") or ".." in local_part:
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return False
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# (5.) Validate the characters in the domain
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if any(char not in string.ascii_letters + string.digits + ".-" for char in domain):
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return False
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# (6.) Validate the placement of "-" characters
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if domain.startswith("-") or domain.endswith("."):
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return False
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# (7.) Validate the placement of "." characters
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return not (domain.startswith(".") or domain.endswith(".") or ".." in domain)
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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for email, valid in email_tests:
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is_valid = is_valid_email_address(email)
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assert is_valid == valid, f"{email} is {is_valid}"
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print(f"Email address {email} is {'not ' if not is_valid else ''}valid")
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