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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def validate(ticket):
 """ Will attempt to validate the ticket. If validation fails, then False is returned. If validation is successful, then True is returned and the validated username is saved in the session under the key `CAS_USERNAME_SESSION_KEY` while tha validated attributes dictionary is saved under the key 'CAS_ATTRIBUTES_SESSION_KEY'. """


    cas_username_session_key = current_app.config['CAS_USERNAME_SESSION_KEY']
    cas_attributes_session_key = current_app.config['CAS_ATTRIBUTES_SESSION_KEY']

    current_app.logger.debug("validating token {0}".format(ticket))

    cas_validate_url = create_cas_validate_url(
        current_app.config['CAS_SERVER'],
        current_app.config['CAS_VALIDATE_ROUTE'],
        flask.url_for('.login', origin=flask.session.get('CAS_AFTER_LOGIN_SESSION_URL'), _external=True),
        ticket)

    current_app.logger.debug("Making GET request to {0}".format(
        cas_validate_url))

    xml_from_dict = {}
    isValid = False

    try:
        xmldump = urlopen(cas_validate_url).read().strip().decode('utf8', 'ignore')
        xml_from_dict = parse(xmldump)
        isValid = True if "cas:authenticationSuccess" in xml_from_dict["cas:serviceResponse"] else False
    except ValueError:
        current_app.logger.error("CAS returned unexpected result")

    if isValid:
        current_app.logger.debug("valid")
        xml_from_dict = xml_from_dict["cas:serviceResponse"]["cas:authenticationSuccess"]
        username = xml_from_dict["cas:user"]
        flask.session[cas_username_session_key] = username

        if "cas:attributes" in xml_from_dict:
            attributes = xml_from_dict["cas:attributes"]

            if "cas:memberOf" in attributes:
                attributes["cas:memberOf"] = attributes["cas:memberOf"].lstrip('[').rstrip(']').split(',')
                for group_number in range(0, len(attributes['cas:memberOf'])):
                    attributes['cas:memberOf'][group_number] = attributes['cas:memberOf'][group_number].lstrip(' ').rstrip(' ')

            flask.session[cas_attributes_session_key] = attributes
    else:
        current_app.logger.debug("invalid")

    return isValid