SF 582071 clarified the .split() method's docstring to note that sep=None
will trigger splitting on any whitespace.
diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index c40bc18..3c1b303 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -1126,8 +1126,8 @@
\n\
Return a list of the words in the string S, using sep as the\n\
delimiter string. If maxsplit is given, at most maxsplit\n\
-splits are done. If sep is not specified, any whitespace string\n\
-is a separator.");
+splits are done. If sep is not specified or is None, any\n\
+whitespace string is a separator.");
static PyObject *
string_split(PyStringObject *self, PyObject *args)