You can choose to program functionally in Java or Python! I do this enough that seeing object oriented Python irritates me. I see this as more of a stylistic choice than forcing new languages.
It's nearly always better for the project to choose a widely known and supported language, which will be Java or Python or some such. But learning how much can be done functionally when the language compels you to changes the way you look at it even when the language has imperative features.
you cannot write Python like Haskell (for example) because Python lacks the necessary features.