Note: It seems like I am about to run out of the free quota (I see the usage as 754K characters already). I grossly underestimated.

Edit: If I run out of the quota, which it looks like I will, you can use your own API key locally by using this package: https://pypi.python.org/pypi/ulit/. A neat feature is that you can use Google translate API as well but it is not nearly as much fun.

Update: I ran out of the quota but have emailed Yandex if I can pay a few bucks to keep it running. It seems to have under 50 mil characters, you pay about $15.