Python - wget check when process has completed

I have a function that is calling wget via subprocess.Popen. The purpose of this function is to spawn wget and spider a website for a list of links.

Is it possible to tell when the wget process has completed and then continue executing the rest of the python function e.g.

def get_urls(url, uname, pword, output):    subprocess.Popen (['wget', '-nd', '-r', '--user=', uname, '--password=', pword,  '--no-parent','--spider',url, '--output-file= ',output], stdout=subprocess.PIPE)    #some method telling wget has finished writing to the output file, so continue    foo = bar() #rest of function etc.

Also is there a better method of spidering a site (and passing in login credentials) via python rather than making system calls?

Thanks