Issue #26801: shutil.get_terminal_size() now handles the case of stdout is

reopened on Windows.  Added tests for fallbacks.

Lib/shutil.py

@@ -1069,7 +1069,9 @@ def get_terminal_size(fallback=(80, 24)):
     if columns <= 0 or lines <= 0:
         try:
             size = os.get_terminal_size(sys.__stdout__.fileno())
-        except (AttributeError, OSError):
+        except (AttributeError, ValueError, OSError):
+            # stdout is None, closed, detached, or not a terminal, or
+            # os.get_terminal_size() is unsupported
             size = os.terminal_size(fallback)
         if columns <= 0:
             columns = size.columns

Lib/test/test_shutil.py

@@ -1828,14 +1828,24 @@ class TermsizeTests(unittest.TestCase):
 
         with support.EnvironmentVarGuard() as env:
             env['COLUMNS'] = '777'
+            del env['LINES']
             size = shutil.get_terminal_size()
         self.assertEqual(size.columns, 777)
 
         with support.EnvironmentVarGuard() as env:
+            del env['COLUMNS']
             env['LINES'] = '888'
             size = shutil.get_terminal_size()
         self.assertEqual(size.lines, 888)
 
+    def test_bad_environ(self):
+        with support.EnvironmentVarGuard() as env:
+            env['COLUMNS'] = 'xxx'
+            env['LINES'] = 'yyy'
+            size = shutil.get_terminal_size()
+        self.assertGreaterEqual(size.columns, 0)
+        self.assertGreaterEqual(size.lines, 0)
+
     @unittest.skipUnless(os.isatty(sys.__stdout__.fileno()), "not on tty")
     @unittest.skipUnless(hasattr(os, 'get_terminal_size'),
                          'need os.get_terminal_size()')
@@ -1859,6 +1869,25 @@ class TermsizeTests(unittest.TestCase):
 
         self.assertEqual(expected, actual)
 
+    def test_fallback(self):
+        with support.EnvironmentVarGuard() as env:
+            del env['LINES']
+            del env['COLUMNS']
+
+            # sys.__stdout__ has no fileno()
+            with support.swap_attr(sys, '__stdout__', None):
+                size = shutil.get_terminal_size(fallback=(10, 20))
+            self.assertEqual(size.columns, 10)
+            self.assertEqual(size.lines, 20)
+
+            # sys.__stdout__ is not a terminal on Unix
+            # or fileno() not in (0, 1, 2) on Windows
+            with open(os.devnull, 'w') as f, \
+                 support.swap_attr(sys, '__stdout__', f):
+                size = shutil.get_terminal_size(fallback=(30, 40))
+            self.assertEqual(size.columns, 30)
+            self.assertEqual(size.lines, 40)
+
 
 class PublicAPITests(unittest.TestCase):
     """Ensures that the correct values are exposed in the public API."""