I suspect that I found a bug. If I run the following script:

```
def f(t=None):
    t0, t1 = t if t is not None else [], []
    return t0, t1


def g(t=None):
    if t is None:
        t = [], []
    t0, t1 = t
    return t0, t1


def test():
    res_f = f(t=([1, 1], [2, 2]))
    res_g = g(t=([1, 1], [2, 2]))
    assert res_f == res_g, f'{res_f=} != {res_g=}'


test()
```

I get an assertion error, with:

```
res_f=(([1, 1], [2, 2]), []) != res_g=([1, 1], [2, 2])
```

I expected them to be equal.

This is a operation precedence issue.

The line:

    t0, t1 = t if t is not None else [], []

is parsed as:

    (t if t is not None else []), []


so you need brackets around the "else" operand to get the effect you want.

    t0, t1 = t if t is not None else ([], [])