Issue #16120: Use |yield from| in stdlib.

Patch by Berker Peksag.

Lib/lib2to3/btm_utils.py

@@ -96,8 +96,7 @@ class MinNode(object):
     def leaves(self):
         "Generator that returns the leaves of the tree"
         for child in self.children:
-            for x in child.leaves():
+            yield from child.leaves()
-                yield x
         if not self.children:
             yield self
 
@@ -277,7 +276,6 @@ def rec_test(sequence, test_func):
     sub-iterables"""
     for x in sequence:
         if isinstance(x, (list, tuple)):
-            for y in rec_test(x, test_func):
+            yield from rec_test(x, test_func)
-                yield y
         else:
             yield test_func(x)

Lib/lib2to3/pytree.py

@@ -194,8 +194,7 @@ class Base(object):
 
     def leaves(self):
         for child in self.children:
-            for x in child.leaves():
+            yield from child.leaves()
-                yield x
 
     def depth(self):
         if self.parent is None:
@@ -274,16 +273,14 @@ class Node(Base):
     def post_order(self):
         """Return a post-order iterator for the tree."""
         for child in self.children:
-            for node in child.post_order():
+            yield from child.post_order()
-                yield node
         yield self
 
     def pre_order(self):
         """Return a pre-order iterator for the tree."""
         yield self
         for child in self.children:
-            for node in child.pre_order():
+            yield from child.pre_order()
-                yield node
 
     def _prefix_getter(self):
         """

Lib/unittest/loader.py

@@ -291,8 +291,7 @@ class TestLoader(object):
                         # tests loaded from package file
                         yield tests
                     # recurse into the package
-                    for test in self._find_tests(full_path, pattern):
+                    yield from self._find_tests(full_path, pattern)
-                        yield test
                 else:
                     try:
                         yield load_tests(self, tests, pattern)