Add a prepend() recipe to teach a chain() idiom (GH-6415)

1 files changed, 5 insertions, 0 deletions

diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index a5a5356..959424f 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -688,6 +688,11 @@ which incur interpreter overhead.
        "Return first n items of the iterable as a list"
        return list(islice(iterable, n))
 
+   def prepend(value, iterator):
+       "Prepend a single value in front of an iterator"
+       # prepend(1, [2, 3, 4]) -> 1 2 3 4
+       return chain([value], iterator)
+
    def tabulate(function, start=0):
        "Return function(0), function(1), ..."
        return map(function, count(start))