Mwlib with only one line: "No JSON object could be decoded"

Heck, I'm trying to use mwlib (like they describe here), I've only two lines, like in the tutorial:

import mwclient
site = mwclient.Site('', path='/wiki/')

And I got an error "No JSON object could be decoded". How on the earth can a one line program have an error ???

Most likely, you're using URL rewriting to get short URL (like /wiki/Nice_page, rather than /mediawiki?index.php?title=Nice_page). To use API, you must access the real path, that is /mediawiki/api.php