Fix and add test for itertools.zip_longest

Author: timfel

graalpython/com.oracle.graal.python.test/src/tests/test_iterator.py

@@ -122,3 +122,10 @@ def test_iterator_in():
     assert 1 in (i for i in range(2))
     assert 1 in iter(range(2))
     assert 1 not in iter(range(1))
+
+
+def test_itertools_zip_longest():
+    from itertools import zip_longest
+    x = [1,2,3]
+    y = [4,5,6,7]
+    assert list(zip_longest(x,y)) == [(1, 4), (2, 5), (3, 6), (None, 7)], list(zip_longest(x,y))

graalpython/lib-graalpython/itertools.py

@@ -637,11 +637,14 @@ def __next__(self):
         nb = len(self.iterators)
         if nb == 0:
             raise StopIteration
-        return tuple(self._fetch(index) for index in range(nb))
+        result = []
+        for index in range(nb):
+            result.append(self._fetch(index))
+        return tuple(result)
 
     def __new__(subtype, iter1, *args, fillvalue=None):
         self = object.__new__(subtype)
         self.fillvalue = fillvalue
         self.active = len(args) + 1
-        self.iterators = [iter1] + args
+        self.iterators = [iter(iter1)] + [iter(arg) for arg in args]
         return self