Checking whole string with a regex

I'm trying to check if a string is a number, so the regex "\d+" seemed good. However that regex also fits "78.46.92.168:8000" for some reason, which I do not want, a little bit of code:

class Foo():
    _rex = re.compile("\d+")
    def bar(self, string):
         m = _rex.match(string)
         if m != None:
             doStuff()

And doStuff() is called when the ip adress is entered. I'm kind of confused, how does "." or ":" match "\d"?