error installing nltk supporting packages : nltk.download()

Try below code. It has downloaded package as expected

import nltk
import ssl

try:
    _create_unverified_https_context = ssl._create_unverified_context
except AttributeError:
    pass
else:
    ssl._create_default_https_context = _create_unverified_https_context

nltk.download()

Looks before link was broken whicvh been fixed by ssl.

Note :- MAC been used

I got this error because of network constraint. Here is how I solved

Browsed http://www.nltk.org/nltk_data/ and downloaded required corpora from the corresponding link.

Then placed the downloaded files in C:/ folder path in windows (or any other relevant directories like C:/ProgramData/Anaconda3) in a same folder structure mentioned in https://github.com/nltk/nltk_data/tree/gh-pages/packages

Got the solution. The issue in my case was that when the NLTK downloader started it had the server index as - http://nltk.github.com/nltk_data/

This needs to be changed to - http://nltk.org/nltk_data/

You can change this by going into the NLTK Downloader window and the File->Change Server Index.

Regards, Bonson