User Home Dir

os.path

You want to use os.path.expanduser.

This will ensure it works on all platforms:

from os.path import expanduser
home = expanduser("~")

pathlib.Path

If you're on Python 3.5+ you can use pathlib.Path.home():

from pathlib import Path
home = str(Path.home())

But it's usually better not to convert Path.home() to string. It's more natural to use this way:

with open(Path.home() / ".ssh" / "known_hosts") as f:
    lines = f.readlines()