gh-128136: Possibility to customize hardcoded xml declaration

Lib/test/test_xml_etree.py

@@ -4021,6 +4021,54 @@ def test_write_to_user_binary_writer_with_bom(self):
                 '''<?xml version='1.0' encoding='utf-16'?>\n'''
                 '''<site />'''.encode("utf-16"))
 
+    def test_custom_declaration_to_user_binary_writer_with_bom(self):
+        tree = ET.ElementTree(ET.XML('''<site />'''))
+        raw = io.BytesIO()
+        writer = self.dummy()
+        writer.write = raw.write
+        writer.seekable = lambda: True
+        writer.tell = raw.tell
+        tree.write(writer, encoding="utf-16", xml_declaration_definition='<?xml version="{version}" encoding="{encoding}"?>')
+        self.assertEqual(raw.getvalue(),
+                '''<?xml version="1.0" encoding="utf-16"?>\n'''
+                '''<site />'''.encode("utf-16"))
+
+    def test_custom_declaration2_to_user_binary_writer_with_bom(self):
+        tree = ET.ElementTree(ET.XML('''<site />'''))
+        raw = io.BytesIO()
+        writer = self.dummy()
+        writer.write = raw.write
+        writer.seekable = lambda: True
+        writer.tell = raw.tell
+        tree.write(writer, encoding="utf-16", xml_declaration_definition='<?xml version="1.1" encoding="{encoding}"?>')
+        self.assertEqual(raw.getvalue(),
+                '''<?xml version="1.1" encoding="utf-16"?>\n'''
+                '''<site />'''.encode("utf-16"))
+
+    def test_custom_declaration3_to_user_binary_writer_with_bom(self):
+        tree = ET.ElementTree(ET.XML('''<site />'''))
+        raw = io.BytesIO()
+        writer = self.dummy()
+        writer.write = raw.write
+        writer.seekable = lambda: True
+        writer.tell = raw.tell
+        tree.write(writer, encoding="utf-16", xml_declaration_definition='<?xml version="1.1" encoding="UTF-8"?>')
+        self.assertEqual(raw.getvalue(),
+                '''<?xml version="1.1" encoding="UTF-8"?>\n'''
+                '''<site />'''.encode("utf-16"))
+
+    def test_custom_declaration4_to_user_binary_writer_with_bom(self):
+        tree = ET.ElementTree(ET.XML('''<site />'''))
+        raw = io.BytesIO()
+        writer = self.dummy()
+        writer.write = raw.write
+        writer.seekable = lambda: True
+        writer.tell = raw.tell
+        tree.write(writer, encoding="utf-16", xml_declaration_definition='<?xml version="1.0"?>')
+        self.assertEqual(raw.getvalue(),
+                '''<?xml version="1.0"?>\n'''
+                '''<site />'''.encode("utf-16"))
+
     def test_tostringlist_invariant(self):
         root = ET.fromstring('<tag>foo</tag>')
         self.assertEqual(

Lib/xml/etree/ElementTree.py

@@ -681,7 +681,8 @@ def write(self, file_or_filename,
               xml_declaration=None,
               default_namespace=None,
               method=None, *,
-              short_empty_elements=True):
+              short_empty_elements=True,
+              xml_declaration_definition="<?xml version='{version}' encoding='{encoding}'?>"):
         """Write element tree to a file as XML.
 
         Arguments:
@@ -694,6 +695,14 @@ def write(self, file_or_filename,
                                is added if encoding IS NOT either of:
                                US-ASCII, UTF-8, or Unicode
 
+          *xml_declaration_definition* -- string for customizing encoding declaration
+                                          as documentation always shows doublequotes but
+                                          singlequote where hardcoded here.
+                                          to be rfc conform which allows doublequotes and
+                                          singlequote for declaration. default value is
+                                          untouched to pass tests.
+                                          placeholders: {version}, {encoding}
+
           *default_namespace* -- sets the default XML namespace (for "xmlns")
 
           *method* -- either "xml" (default), "html, "text", or "c14n"
@@ -719,8 +728,10 @@ def write(self, file_or_filename,
                     (xml_declaration is None and
                      encoding.lower() != "unicode" and
                      declared_encoding.lower() not in ("utf-8", "us-ascii"))):
-                write("<?xml version='1.0' encoding='%s'?>\n" % (
-                    declared_encoding,))
+                # version configuration is'nt necessary, can be overwritten
+                # in declaration_definition at runtime
+                data = {'version':'1.0', 'encoding': declared_encoding}
+                write(xml_declaration_definition.format(**data)+"\n")
             if method == "text":
                 _serialize_text(write, self._root)
             else:

Misc/NEWS.d/next/Library/2024-12-20-18-54-53.gh-issue-128136.tgbvWt.rst

@@ -0,0 +1,8 @@
+New parameter added to the write function that allows you to customize the xml declaration, which was previously hard-coded.
+The standard functionality is retained; if you don't specify the xml_declaration_definition parameter, the previous standard declaration is used. ``<?xml version='1.0' encoding='{encoding}'?>``
+When specifying the parameter, the following options are available.
+E.g.:
+tree.write(file, encoding="utf-8", xml_declaration=True, xml_declaration_definition='''<?xml version="{version}" encoding="{encoding}"?>''')
+tree.write(file, encoding="utf-8", xml_declaration=True, xml_declaration_definition='''<?xml version="1.1" encoding="{encoding}"?>''')
+tree.write(file, encoding="utf-8", xml_declaration=True, xml_declaration_definition='''<?xml version="1.1"?>''')
+The placeholders {version} and {encoding} are replaced, version is always 1.0 and enconding depends on the code as before.