bpo-40806: Clarify that itertools.product immediately consumes its inpt (GH-20492)

stsouko · web-flow · commit cfc6ce4d40f2 · 2020-05-28T09:46:22.000-07:00
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
@@ -563,6 +563,9 @@ loops that truncate the stream.
            for prod in result:
                yield tuple(prod)
 
+   Before :func:`product` runs, it completely consumes the input iterables,
+   keeping pools of values in memory to generate the products.  Accordingly,
+   it only useful with finite inputs.
 
 .. function:: repeat(object[, times])
 
