this was my code
from pytube import YouTube
a=YouTube("https://www.youtube.com/watch?v=vvpb8IdDZZI")
#to print title
print("\n")
print("******************title*****************")
print("the title is:"+a.title)
the error was
raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 404: Not Found
but the url exists!!!and i have copied this url from browser itself and i have also upgraded my pytube