Apply Seirhy suggestions

Author: StanFromIreland

Lib/test/test_tools/test_msgfmt.py

@@ -39,6 +39,14 @@ def test_compilation(self):
 
                     self.assertDictEqual(actual._catalog, expected._catalog)
 
+    def test_po_with_bom(self):
+        with temp_cwd():
+            Path('bom.po').write_bytes(b'\xef\xbb\xbfmsgid "Python"\nmsgstr "Pioton"\n')
+
+            res = assert_python_failure(msgfmt, 'bom.po')
+            err = res.err.decode('utf-8')
+            self.assertIn('The file bom.po starts with a UTF-8 BOM', err)
+
     def test_invalid_msgid_plural(self):
         with temp_cwd():
             Path('invalid.po').write_text('''\

Tools/i18n/msgfmt.py

@@ -35,6 +35,8 @@
 
 __version__ = "1.2"
 
+import codecs
+
 MESSAGES = {}
 
 
@@ -117,7 +119,7 @@ def make(filename, outfile):
         sys.exit(1)
 
     # Check for UTF-8 BOM
-    if lines[0].startswith(b'\xef\xbb\xbf'):
+    if lines[0].startswith(codecs.BOM_UTF8):
         print(
             f"The file {infile} starts with a UTF-8 BOM which is not allowed in .po files.\n"
             "Please save the file without a BOM and try again.",