<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _root_domain():
 """ Deduce the root domain name - usually a 'naked' domain. This only needs to be done prior to the first deployment """


    if not hasattr(env,'root_domain'):
        cwd = os.getcwd().split(os.sep)
        domain = ''
        #if the first env.host has a domain name then we'll use that
        #since there are no top level domains that have numbers in them we can test env.host

        username, host, port = normalize(env.hosts[0])
        if host[-1] in string.ascii_letters:
            domain_parts = env.host.split('.')
            length = len(domain_parts)
            if length==2:
                #assumes .com .net etc so we want the full hostname for the domain
                domain = host
            elif length==3 and len(domain_parts[-1])==2:
                #assume country tld so we want the full hostname for domain
                domain = host
            elif length >=3:
                #assume the first part is the hostname of the machine
                domain = '.'.join(domain[1:])
        #we'll just pick the first directory in the path which has a period.
        else:
            for d in cwd:
                if '.' in d: 
                    domain = d
        if not domain and env.INTERACTIVE:
            domain = prompt('Enter the root domain for this project ',default='example.com')
        else:
            domain = 'example.com'
        env.root_domain = domain
    return env.root_domain