circuitpython/tests/basics/io_iobase.py

try:
    import uio as io
except:
    import io

try:
    io.IOBase
except AttributeError:
    print("SKIP")
    raise SystemExit


class MyIO(io.IOBase):
    def write(self, buf):
        # CPython and uPy pass in different types for buf (str vs bytearray)
        print("write", len(buf))
        return len(buf)


print("test", file=MyIO())