Address review feedback: revert stderr routing, update docs and tests

Per sobolevn's review: revert the behavior change that routed error
messages to stderr, as existing code may rely on stdout behavior.
Instead update docs to accurately reflect that errors go to stdout.

Also update tests to assert full output contents as suggested.

Author: htjworld

Doc/library/mimetypes.rst

@@ -348,7 +348,7 @@ it converts file extensions to MIME types.
 
 For each ``type`` entry, the script writes a line into the standard output
 stream. If an unknown type occurs, it writes an error message into the
-standard error stream and exits with the return code ``1``.
+standard output stream and exits with the return code ``1``.
 
 
 .. mimetypes-cli-example:

Lib/mimetypes.py

@@ -756,11 +756,5 @@ def _main(args=None):
     import sys
 
     results = _main()
-    has_error = False
-    for result in results:
-        if result.startswith("error: "):
-            print(result, file=sys.stderr, flush=True)
-            has_error = True
-        else:
-            print(result, flush=True)
-    sys.exit(has_error)
+    print("\n".join(results))
+    sys.exit(any(result.startswith("error: ") for result in results))

Lib/test/test_mimetypes.py

@@ -519,13 +519,13 @@ def test_help(self):
 
     def test_type_lookup(self):
         rc, stdout, stderr = assert_python_ok('-m', 'mimetypes', 'foo.pdf')
-        self.assertIn(b'application/pdf', stdout)
+        self.assertEqual(stdout.strip(), b'type: application/pdf encoding: None')
         self.assertEqual(stderr, b'')
 
     def test_type_lookup_unknown(self):
         rc, stdout, stderr = assert_python_failure('-m', 'mimetypes', 'foo.unknownext12345')
-        self.assertEqual(stdout, b'')
-        self.assertIn(b'error:', stderr)
+        self.assertEqual(stdout.strip(), b'error: media type unknown for foo.unknownext12345')
+        self.assertEqual(stderr, b'')
 
     def test_extension_flag(self):
         rc, stdout, stderr = assert_python_ok('-m', 'mimetypes', '-e', 'image/jpeg')
@@ -534,8 +534,8 @@ def test_extension_flag(self):
 
     def test_extension_flag_unknown(self):
         rc, stdout, stderr = assert_python_failure('-m', 'mimetypes', '-e', 'image/unknowntype12345')
-        self.assertEqual(stdout, b'')
-        self.assertIn(b'error:', stderr)
+        self.assertEqual(stdout.strip(), b'error: unknown type image/unknowntype12345')
+        self.assertEqual(stderr, b'')
 
     def test_lenient_flag(self):
         rc, stdout, stderr = assert_python_ok('-m', 'mimetypes', '-e', '--lenient', 'text/xul')
@@ -544,17 +544,17 @@ def test_lenient_flag(self):
 
     def test_multiple_inputs(self):
         rc, stdout, stderr = assert_python_ok('-m', 'mimetypes', 'foo.pdf', 'foo.png')
-        self.assertIn(b'application/pdf', stdout)
-        self.assertIn(b'image/png', stdout)
+        self.assertIn(b'type: application/pdf encoding: None', stdout)
+        self.assertIn(b'type: image/png encoding: None', stdout)
         self.assertEqual(stderr, b'')
 
     def test_multiple_inputs_with_error(self):
         rc, stdout, stderr = assert_python_failure(
             '-m', 'mimetypes', 'foo.pdf', 'foo.unknownext12345'
         )
-        self.assertIn(b'application/pdf', stdout)
-        self.assertNotIn(b'error:', stdout)
-        self.assertIn(b'error:', stderr)
+        self.assertIn(b'type: application/pdf encoding: None', stdout)
+        self.assertIn(b'error: media type unknown for foo.unknownext12345', stdout)
+        self.assertEqual(stderr, b'')
 
     def test_unknown_flag(self):
         rc, stdout, stderr = assert_python_failure('-m', 'mimetypes', '--unknown-flag')