task #5

#!/usr/bin/env python
import re


class CheckEmailErr(Exception):
    pass

class InvalidHostErr(CheckEmailErr):
    pass

class InvalidNameErr(CheckEmailErr):
    pass

class AtIsNotOnceErr(CheckEmailErr):
    pass


def checkHost(host):
    if not re.compile("^[a-z0-9_.-]{3,256}$").match(host):
        raise InvalidHostErr
    items = host.split(".")
    if len(items) < 2:
        raise InvalidHostErr
    for item in items:
        if not item or item[0] == "-" or item[-1] == "-":
            raise InvalidHostErr


def checkName(name):
    if not re.compile("^[a-z0-9\"._!,:-]{,128}$").match(name):
        raise InvalidNameErr
    quote = False
    if name.find("..") != -1:
        raise InvalidNameErr
    for c in name:
        if c == "\"":
            quote = not quote
        elif c in "!,:":
            if not quote:
                raise InvalidNameErr
    if quote:
        raise InvalidNameErr


def isValidEmail(email):
    try:
        items = email.split("@")
        if len(items) != 2:
            raise AtIsNotOnceErr
        name, host = items
        checkHost(host)
        checkName(name)
        return True
    except CheckEmailErr:
        return False