As mentioned, there's CircuitPython and MicroPython, each with its "native" boards. The difference, to the best of my knowledge, is that MicroPython was optimized specifically for MCUs in some ways, while CircuitPython tries to stay true(r) to the original Python syntax.
Both are very limited. Obviously you can't just import any Python library, and what you do have will be slow and heavy on the microcontrollers' resources. I've done a couple of little demo projects on the BBC Micro:bit and a Pyboard clone from China. It's fun, arguably excellent for getting children interested in embedded/programming, but for more serious work you'll hit the limitations of these languages very fast.