bpo-31082: Use "iterable" in the docstring for functools.reduce() (GH-20796)

diff --git a/Modules/_functoolsmodule.c b/Modules/_functoolsmodule.c
index 8120140..bb86fe8 100644
--- a/Modules/_functoolsmodule.c
+++ b/Modules/_functoolsmodule.c
@@ -679,7 +679,7 @@
 
     if (result == NULL)
         PyErr_SetString(PyExc_TypeError,
-                   "reduce() of empty sequence with no initial value");
+                   "reduce() of empty iterable with no initial value");
 
     Py_DECREF(it);
     return result;
@@ -692,14 +692,14 @@
 }
 
 PyDoc_STRVAR(functools_reduce_doc,
-"reduce(function, sequence[, initial]) -> value\n\
+"reduce(function, iterable[, initial]) -> value\n\
 \n\
-Apply a function of two arguments cumulatively to the items of a sequence,\n\
-from left to right, so as to reduce the sequence to a single value.\n\
-For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates\n\
+Apply a function of two arguments cumulatively to the items of a sequence\n\
+or iterable, from left to right, so as to reduce the iterable to a single\n\
+value.  For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates\n\
 ((((1+2)+3)+4)+5).  If initial is present, it is placed before the items\n\
-of the sequence in the calculation, and serves as a default when the\n\
-sequence is empty.");
+of the iterable in the calculation, and serves as a default when the\n\
+iterable is empty.");
 
 /* lru_cache object **********************************************************/