I know this is old... so some stuff might have changed and be changing... but as for the time of this comment :

 from steem.steemd import Steemd 

^This is critical for making that stuff work.

Once more I might be doing this all wrong but I think the steem-python libraries require you do it like this:

import steem
from steem import Steem
from steem.post import Post
from steem.steemd import Steemd
stmd = Steemd()
#....
#....
post = Post('permlink', stmd)
# or this might also work:
post = Post('permlink', Steemd())