ifnoneは、coreの関数

def ifnone(a:Any,b:Any)->Any:
    "`a` if `a` is not None, otherwise `b`."
    return b if a is None else a

https://github.com/fastai/fastai/blob/master/fastai/core.py

「aがNoneでなければa、そうでなければbです。」

def test_ifnone():
    assert ifnone(None, 5) == 5
    assert ifnone(5, None) == 5
    assert ifnone(1, 5)    == 1
    assert ifnone(0, 5)    == 0

https://github.com/fastai/fastai/blob/master/tests/test_core.py