Update "clock" without freezing program

[JoshuaBurleson]

Just fooling around I came across an issue updating a digital-clock like label. This:

self.now=time.strftime('%a. %b %d %Y %H:%M:%S',time.localtime())
        self.clock=ttk.Label(self,text=self.now)
        self.clock.pack()
        while True:
            self.now=time.strftime('%a. %b %d %Y %H:%M:%S',time.localtime())
            self.clock['text']=self.now

simply freezes the program, I've managed to get it to update on certain events like the user hitting a button but I'd like it to continuously update. Any ideas?

EDIT: I got this to work using configure, but why does that work and not this?
Double EDIT:After some thinking I decided it was because the program was stuck in an infinite while loop, however this simply revisits the method.

[TrustyTony]

You are using after timer events as demonstrated in by color changing label demo snippet?

[JoshuaBurleson]

No, I just checked out similar clocks on tkinter using the power of google, I didn't even think to go to the color changing one :(