gh-153782: Make traceback.print_list() delegate to format_list()

print_list() and format_list() each formatted a StackSummary with the
same expression, so their outputs agreed only by duplication. Route
print_list() through format_list() so print_list(x), keeping the two
public helpers from drifting, and add a regression test that
print_list() matches format_list() for tuple, FrameSummary, and
StackSummary inputs.

Author: basil

Lib/test/test_traceback.py

@@ -3431,6 +3431,23 @@ def test_format_smoke(self):
             ['  File "foo.py", line 1, in fred\n    line\n'],
             s.format())
 
+    def test_print_list_matches_format_list(self):
+        frame = traceback.FrameSummary('foo.py', 1, 'fred', line='line')
+        inputs = [
+            ('tuple', [('foo.py', 1, 'fred', 'line')]),
+            ('FrameSummary', [frame]),
+            ('StackSummary',
+             traceback.StackSummary.from_list([('foo.py', 1, 'fred', 'line')])),
+        ]
+        for input_type, extracted_list in inputs:
+            with self.subTest(input_type=input_type):
+                file = StringIO()
+                traceback.print_list(extracted_list, file=file)
+                self.assertEqual(
+                    file.getvalue(),
+                    ''.join(traceback.format_list(extracted_list)),
+                )
+
     def test_locals(self):
         linecache.updatecache('/foo.py', globals())
         c = test_code('/foo.py', 'method')

Lib/traceback.py

@@ -72,7 +72,7 @@ def print_list(extracted_list, file=None):
     extract_stack() as a formatted stack trace to the given file."""
     if file is None:
         file = sys.stderr
-    for item in StackSummary.from_list(extracted_list).format():
+    for item in format_list(extracted_list):
         print(item, file=file, end="")
 
 def format_list(extracted_list):

Misc/ACKS

@@ -404,6 +404,7 @@ Laura Creighton
 Nick Crews
 Tyler Crompton
 Simon Cross
+Basil Crow
 Felipe Cruz
 Drew Csillag
 Alessandro Cucci