Steemit Inc. just changed the address of their API-node.
It used to be:
https://steemd.steemit.com
Now it is:
https://api.steemit.com
There are different methods to change the default nodes Steem-Python connects to.
The proper way is this: https://steemit.com/witness/@themarkymark/fix-witness-price-feed-if-using-conductor
If you don't use steempy at all and just want to fix your scripts, edit this file:
/.local/lib/python3.5/site-packages/steem/steemd.py
In line 53, change https://steemd.steemit.com to your favourite node(s).