From 4edc95cf0a2960431621eee9bc194f6225f1690b Mon Sep 17 00:00:00 2001
From: Shantanu <hauntsaninja@users.noreply.github.com>
Date: Sun, 1 Mar 2020 22:33:24 -0800
Subject: [PATCH] bpo-39495: Remove default value from C impl of
 TreeBuilder.start (GH-18275)

---
 Lib/test/test_xml_etree.py                         |  4 ++++
 .../2020-01-30-07-02-02.bpo-39495.8LsIRN.rst       |  1 +
 Modules/_elementtree.c                             |  4 ++--
 Modules/clinic/_elementtree.c.h                    | 14 +++++++-------
 4 files changed, 14 insertions(+), 9 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2020-01-30-07-02-02.bpo-39495.8LsIRN.rst

diff --git a/Lib/test/test_xml_etree.py b/Lib/test/test_xml_etree.py
index 09c234ca689..785edb73702 100644
--- a/Lib/test/test_xml_etree.py
+++ b/Lib/test/test_xml_etree.py
@@ -2259,6 +2259,10 @@ class BugsTest(unittest.TestCase):
         text = text[6:-4]
         self.assertEqual(root.get('b'), text)
 
+    def test_39495_treebuilder_start(self):
+        self.assertRaises(TypeError, ET.TreeBuilder().start, "tag")
+        self.assertRaises(TypeError, ET.TreeBuilder().start, "tag", None)
+
 
 
 # --------------------------------------------------------------------
diff --git a/Misc/NEWS.d/next/Library/2020-01-30-07-02-02.bpo-39495.8LsIRN.rst b/Misc/NEWS.d/next/Library/2020-01-30-07-02-02.bpo-39495.8LsIRN.rst
new file mode 100644
index 00000000000..116a5187c2e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-01-30-07-02-02.bpo-39495.8LsIRN.rst
@@ -0,0 +1 @@
+Remove default value from *attrs* parameter of :meth:`xml.etree.ElementTree.TreeBuilder.start` for consistency between Python and C implementations.
diff --git a/Modules/_elementtree.c b/Modules/_elementtree.c
index 4498c5ffd54..c0f771f7d93 100644
--- a/Modules/_elementtree.c
+++ b/Modules/_elementtree.c
@@ -3038,7 +3038,7 @@ _elementtree_TreeBuilder_close_impl(TreeBuilderObject *self)
 _elementtree.TreeBuilder.start
 
     tag: object
-    attrs: object = None
+    attrs: object(subclass_of='&PyDict_Type')
     /
 
 [clinic start generated code]*/
@@ -3046,7 +3046,7 @@ _elementtree.TreeBuilder.start
 static PyObject *
 _elementtree_TreeBuilder_start_impl(TreeBuilderObject *self, PyObject *tag,
                                     PyObject *attrs)
-/*[clinic end generated code: output=e7e9dc2861349411 input=95fc1758dd042c65]*/
+/*[clinic end generated code: output=e7e9dc2861349411 input=7288e9e38e63b2b6]*/
 {
     return treebuilder_handle_start(self, tag, attrs);
 }
diff --git a/Modules/clinic/_elementtree.c.h b/Modules/clinic/_elementtree.c.h
index a184b0ffb78..dae5233ee8d 100644
--- a/Modules/clinic/_elementtree.c.h
+++ b/Modules/clinic/_elementtree.c.h
@@ -761,7 +761,7 @@ _elementtree_TreeBuilder_close(TreeBuilderObject *self, PyObject *Py_UNUSED(igno
 }
 
 PyDoc_STRVAR(_elementtree_TreeBuilder_start__doc__,
-"start($self, tag, attrs=None, /)\n"
+"start($self, tag, attrs, /)\n"
 "--\n"
 "\n");
 
@@ -777,17 +777,17 @@ _elementtree_TreeBuilder_start(TreeBuilderObject *self, PyObject *const *args, P
 {
     PyObject *return_value = NULL;
     PyObject *tag;
-    PyObject *attrs = Py_None;
+    PyObject *attrs;
 
-    if (!_PyArg_CheckPositional("start", nargs, 1, 2)) {
+    if (!_PyArg_CheckPositional("start", nargs, 2, 2)) {
         goto exit;
     }
     tag = args[0];
-    if (nargs < 2) {
-        goto skip_optional;
+    if (!PyDict_Check(args[1])) {
+        _PyArg_BadArgument("start", "argument 2", "dict", args[1]);
+        goto exit;
     }
     attrs = args[1];
-skip_optional:
     return_value = _elementtree_TreeBuilder_start_impl(self, tag, attrs);
 
 exit:
@@ -916,4 +916,4 @@ skip_optional:
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=bee26d0735a3fddc input=a9049054013a1b77]*/
+/*[clinic end generated code: output=3ad029ba71f5ae39 input=a9049054013a1b77]*/