Email address validator

import refrom typing import Pattern# Compiled regular expression for performance and reuse.#   • Limits total length to 254 characters (the maximum allowed by RFC 5321).#   • Limits local‑part length to 64 characters.#   • Allows the typical set of characters permitted in the local part.#   • Enforces a domain consisting of labels separated by dots, each label#     starting and ending with an alphanumeric character and optionally#     containing hyphens. The top‑level domain must be at least two letters._EMAIL_REGEX: Pattern[str] = re.compile(    r"^(?=.{1,254}$)(?=.{1,64}@)[A-Za-z0-9!#$%&'*+/=?^_`{|}~-]+"    r"(?:\.[A-Za-z0-9!#$%&'*+/=?^_`{|}~-]+)*"    r"@"    r"(?:[A-Za-z0-9](?:[A-Za-z0-9-]{0,61}[A-Za-z0-9])?\.)+"    r"[A-Za-z]{2,}$")def is_valid_email(email: str) -> bool:    """Validate an email address.    The validation follows a pragmatic subset of RFC 5322 suitable for most    everyday use cases. It checks:      * Overall length (max 254 characters)      * Local‑part length (max 64 characters)      * Allowed characters in the local part      * Proper domain format with at least one dot and a TLD of 2+ letters    Parameters    ----------    email: str        The email address to validate.    Returns    -------    bool        ``True`` if the address matches the pattern, ``False`` otherwise.    """    if not isinstance(email, str):        return False    return _EMAIL_REGEX.fullmatch(email) is not None# ---------------------------------------------------------------------------# Example usage# ---------------------------------------------------------------------------if __name__ == "__main__":    test_addresses = [        "[email protected]",        "[email protected]",        "[email protected]",        "[email protected]",        "invalid-email@",        "@missing-local.org",        "[email protected]",        "toolongdomainpart@" + "a" * 64 + ".com",    ]    for addr in test_addresses:        print(f"{addr!r:50} -> {is_valid_email(addr)}")