Stemmer/lemmatizer for Polish language
There is bunch of lemmatization solutions for polish language. 
One of the best implementation is in polish morphosyntactic analyser, which you can download here.

It has bindings to python, but you have to install them manually. It is "morphosyntactic analyser" which means, that you get all possible lemmas for a given word. If you want also disambiguation, you can use this tool which is provided as docker container.

My team is currently working on implementing polish language support for Spacy, and we will cover lemmatization, so tool with good integration and support will be available soon.