Regex for a subdomain that allows `wwwboys.domain.com`

Question

I need a regex that will give me the following results from each example and I can't seem to get it right:

example.com yields -> nothing / empty

www.example.com yields -> nothing / empty

account.example.com yields -> account

mywww.example.com yields -> mywww

wwwboys.example.com yields -> wwwboys

cool-www.example.com yields -> cool-www

So, it doesn't matter if they use 'www' in the subdomain, but it can't be only 'www'. It can also contain hyphens.

Answer 1

x="""example.com yields -> nothing / empty

www.example.com yields -> nothing / empty

account.example.com yields -> account

mywww.example.com yields -> mywww

wwwboys.example.com yields -> wwwboys

cool-www.example.com yields -> cool-www"""

>>> re.findall("^([A-Za-z0-9-]+)\.(?<!^www\.)[A-Za-z0-9-]+\.[A-Za-z]+",x,re.MULTILINE)
['account', 'mywww', 'wwwboys', 'cool-www']

Answer 2

mystrings="""
example.com
www.example.com
account.example.com
mywww.example.com
wwwboys.example.com
cool-www.example.com
"""

junk=["example.com","www.example.com"]
for url in mystrings.split("\n"):
    if url and not url.strip() in junk:
       print "-->",url.split(".",2)[0]

output

$ ./python.py
--> account
--> mywww
--> wwwboys
--> cool-www

Answer 3

Here's my solution based on ghostdog74's example:

OFF_LIMITS = ('api', 'www', 'secure', 'account')

def get_safe_subdomain_or_none(host):
    subdomain = None
    L = host.split('.')
    if len(L) is 3 and not L[0] in OFF_LIMITS:  # 3 ensures that you don't have a sub-sub domain, and that you don't have just `example.com`
        subdomain = L[0]
    return subdomain