From 6097cd3f49b109c3474f19c30608c0708c1ec85b Mon Sep 17 00:00:00 2001
From: Parfait Gasana <parfait.gasana@gmail.com>
Date: Mon, 1 Mar 2021 21:39:25 -0600
Subject: [PATCH] BUG: Add decl when xml_declaration=True and
 pretty_print=False for etree parser

---
 pandas/io/formats/xml.py           | 21 ++++++++++++++++++++-
 pandas/tests/io/xml/test_to_xml.py | 14 ++++++++------
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/pandas/io/formats/xml.py b/pandas/io/formats/xml.py
index 044b03ba83714..dd68f0f78261e 100644
--- a/pandas/io/formats/xml.py
+++ b/pandas/io/formats/xml.py
@@ -324,7 +324,9 @@ def build_tree(self) -> bytes:
         if self.pretty_print:
             self.out_xml = self.prettify_tree()
 
-        if not self.xml_declaration:
+        if self.xml_declaration:
+            self.out_xml = self.add_declaration()
+        else:
             self.out_xml = self.remove_declaration()
 
         if self.stylesheet is not None:
@@ -416,6 +418,23 @@ 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'
+
+        doc = (
+            self.out_xml
+            if self.out_xml.startswith(b"<?xml")
+            else decl.encode(self.encoding) + self.out_xml
+        )
+
+        return doc
+
     def remove_declaration(self) -> bytes:
         """
         Remove xml declaration.
diff --git a/pandas/tests/io/xml/test_to_xml.py b/pandas/tests/io/xml/test_to_xml.py
index 2026035a23370..97793ce8f65b8 100644
--- a/pandas/tests/io/xml/test_to_xml.py
+++ b/pandas/tests/io/xml/test_to_xml.py
@@ -867,8 +867,7 @@ def test_xml_declaration_pretty_print():
     assert output == expected
 
 
-@td.skip_if_no("lxml")
-def test_no_pretty_print_with_decl():
+def test_no_pretty_print_with_decl(parser):
     expected = (
         "<?xml version='1.0' encoding='utf-8'?>\n"
         "<data><row><index>0</index><shape>square</shape>"
@@ -879,7 +878,7 @@ def test_no_pretty_print_with_decl():
         "</row></data>"
     )
 
-    output = geom_df.to_xml(pretty_print=False, parser="lxml")
+    output = geom_df.to_xml(pretty_print=False, parser=parser)
     output = equalize_decl(output)
 
     # etree adds space for closed tags
@@ -889,8 +888,7 @@ def test_no_pretty_print_with_decl():
     assert output == expected
 
 
-@td.skip_if_no("lxml")
-def test_no_pretty_print_no_decl():
+def test_no_pretty_print_no_decl(parser):
     expected = (
         "<data><row><index>0</index><shape>square</shape>"
         "<degrees>360</degrees><sides>4.0</sides></row><row>"
@@ -900,7 +898,11 @@ def test_no_pretty_print_no_decl():
         "</row></data>"
     )
 
-    output = geom_df.to_xml(xml_declaration=False, pretty_print=False)
+    output = geom_df.to_xml(xml_declaration=False, pretty_print=False, parser=parser)
+
+    # etree adds space for closed tags
+    if output is not None:
+        output = output.replace(" />", "/>")
 
     assert output == expected