CLN: Adjust namespace handling in to_xml

pandas/io/formats/xml.py

@@ -251,18 +251,11 @@ def other_namespaces(self) -> dict:
         """
 
         nmsp_dict: dict[str, str] = {}
-        if self.namespaces and self.prefix is None:
-            nmsp_dict = {
-                "xmlns": n  # noqa: RUF011
-                for p, n in self.namespaces.items()
-                if p != ""
-            }
-
-        if self.namespaces and self.prefix:
+        if self.namespaces:
             nmsp_dict = {
-                "xmlns": n  # noqa: RUF011
+                f"xmlns{p if p=='' else f':{p}'}": n
                 for p, n in self.namespaces.items()
-                if p == ""
+                if n != self.prefix_uri[1:-1]
             }
 
         return nmsp_dict
@@ -365,16 +358,16 @@ def build_tree(self) -> bytes:
                 elem_row = self.build_attribs(d, elem_row)
                 self.build_elems(d, elem_row)
 
-        self.out_xml = tostring(self.root, method="xml", encoding=self.encoding)
+        self.out_xml = tostring(
+            self.root,
+            method="xml",
+            encoding=self.encoding,
+            xml_declaration=self.xml_declaration,
+        )
 
         if self.pretty_print:
             self.out_xml = self.prettify_tree()
 
-        if self.xml_declaration:
-            self.out_xml = self.add_declaration()
-        else:
-            self.out_xml = self.remove_declaration()
-
         if self.stylesheet is not None:
             raise ValueError(
                 "To use stylesheet, you need lxml installed and selected as parser."
@@ -395,8 +388,10 @@ def get_prefix_uri(self) -> str:
                     uri = f"{{{self.namespaces[self.prefix]}}}"
                 except KeyError:
                     raise KeyError(f"{self.prefix} is not included in namespaces")
-            else:
+            elif "" in self.namespaces:
                 uri = f'{{{self.namespaces[""]}}}'
+            else:
+                uri = ""
 
         return uri
 
@@ -418,31 +413,6 @@ def prettify_tree(self) -> bytes:
 
         return dom.toprettyxml(indent="  ", encoding=self.encoding)
 
-    def add_declaration(self) -> bytes:
-        """
-        Add xml declaration.
-
-        This method will add xml declaration of working tree. Currently,
-        xml_declaration is supported in etree starting in Python 3.8.
-        """
-        decl = f'<?xml version="1.0" encoding="{self.encoding}"?>\n'
-
-        return (
-            self.out_xml
-            if self.out_xml.startswith(b"<?xml")
-            else decl.encode(self.encoding) + self.out_xml
-        )
-
-    def remove_declaration(self) -> bytes:
-        """
-        Remove xml declaration.
-
-        This method will remove xml declaration of working tree. Currently,
-        pretty_print is not supported in etree.
-        """
-
-        return self.out_xml.split(b"?>")[-1].strip()
-
 
 class LxmlXMLFormatter(BaseXMLFormatter):
     """
@@ -513,8 +483,10 @@ def get_prefix_uri(self) -> str:
                     uri = f"{{{self.namespaces[self.prefix]}}}"
                 except KeyError:
                     raise KeyError(f"{self.prefix} is not included in namespaces")
-            else:
+            elif "" in self.namespaces:
                 uri = f'{{{self.namespaces[""]}}}'
+            else:
+                uri = ""
 
         return uri
 

pandas/tests/io/xml/test_to_xml.py

@@ -154,7 +154,6 @@ def equalize_decl(doc):
             '<?xml version="1.0" encoding="utf-8"?',
             "<?xml version='1.0' encoding='utf-8'?",
         )
-
     return doc
 
 
@@ -705,6 +704,39 @@ def test_default_namespace(parser, geom_df):
     assert output == expected
 
 
+def test_unused_namespaces(parser, geom_df):
+    expected = """\
+<?xml version='1.0' encoding='utf-8'?>
+<data xmlns:oth="http://other.org" xmlns:ex="http://example.com">
+  <row>
+    <index>0</index>
+    <shape>square</shape>
+    <degrees>360</degrees>
+    <sides>4.0</sides>
+  </row>
+  <row>
+    <index>1</index>
+    <shape>circle</shape>
+    <degrees>360</degrees>
+    <sides/>
+  </row>
+  <row>
+    <index>2</index>
+    <shape>triangle</shape>
+    <degrees>180</degrees>
+    <sides>3.0</sides>
+  </row>
+</data>"""
+
+    output = geom_df.to_xml(
+        namespaces={"oth": "http://other.org", "ex": "http://example.com"},
+        parser=parser,
+    )
+    output = equalize_decl(output)
+
+    assert output == expected
+
+
 # PREFIX
 
 
@@ -750,7 +782,7 @@ def test_missing_prefix_in_nmsp(parser, geom_df):
 def test_namespace_prefix_and_default(parser, geom_df):
     expected = """\
 <?xml version='1.0' encoding='utf-8'?>
-<doc:data xmlns="http://example.com" xmlns:doc="http://other.org">
+<doc:data xmlns:doc="http://other.org" xmlns="http://example.com">
   <doc:row>
     <doc:index>0</doc:index>
     <doc:shape>square</doc:shape>
@@ -778,13 +810,6 @@ def test_namespace_prefix_and_default(parser, geom_df):
     )
     output = equalize_decl(output)
 
-    if output is not None:
-        # etree and lxml differs on order of namespace prefixes
-        output = output.replace(
-            'xmlns:doc="http://other.org" xmlns="http://example.com"',
-            'xmlns="http://example.com" xmlns:doc="http://other.org"',
-        )
-
     assert output == expected