https://stackoverflow.com/questions/45573833/error-in-downloading-nltk-data-errno-11004-getaddrinfo-failed/57273642#57273642
The issue might be of the Proxy that is setup in the system.
instead of:
import nltk
nltk.download()
use:
nltk.set_proxy(‘SYSTEM PROXY’)
nltk.download()
This should solve the problem. And to find the proxy of the system: seach proxy in start option of windows.