> If this new syntax fixes that, I see the value.

It does. The old syntax creates and assigns the variable at compile-time. => does it at execution time.

So this code:

    def foo(bar, baz=[]):
        baz.append(bar)
        return baz
    foo(1)
    foo(2)
    print(foo(3))

would print '[1, 2, 3]'

But this code:

    def foo(bar, baz=>[]):
        baz.append(bar)
        return baz
    foo(1)
    foo(2)
    print(foo(3))

would print '[3]'