Sorting a list containing None

Question Q4.3.6

The built-in function sorted and sequence method sort require that the elements in the sequence be of types that can be compared: they will fail, for example, if a list contains a mixture of strings and numbers. However, it is frequently the case that a list contains numbers and the special value, None (perhaps denoting missing data). Devise a way to sort such a list by passing a lambda function in the argument key; the None values should end up at the end of the sorted list.

Solution Q4.3.6