There were never tests for the fact that list() always returns a *new*
list object, even when the argument is a list, while tuple() may
return a reference to the argument when it is a tuple. Now there are.
except that it always returns Unicode objects.
A new C API PyObject_Unicode() is also provided.
This closes patch #101664.
Written by Marc-Andre Lemburg. Copyright assigned to Guido van Rossum.