diff -r 61bd6974405f Lib/xml/dom/minidom.py
--- a/Lib/xml/dom/minidom.py	Sat Jun 18 04:18:24 2016 +0300
+++ b/Lib/xml/dom/minidom.py	Sat Jun 18 09:38:41 2016 +0300
@@ -78,6 +78,19 @@ class Node(xml.dom.Node):
 if self.childNodes:
 return self.childNodes[-1]
 
+ def _index(self, refChild):
+ childNodes = self.childNodes
+ try:
+ index = self._index_cache
+ if childNodes[index] == refChild:
+ return index
+ except (AttributeError, IndexError):
+ pass
+ try:
+ return childNodes.index(refChild)
+ except ValueError:
+ raise xml.dom.NotFoundErr()
+
 def insertBefore(self, newChild, refChild):
 if newChild.nodeType == self.DOCUMENT_FRAGMENT_NODE:
 for c in tuple(newChild.childNodes):
@@ -92,10 +105,8 @@ class Node(xml.dom.Node):
 if refChild is None:
 self.appendChild(newChild)
 else:
- try:
- index = self.childNodes.index(refChild)
- except ValueError:
- raise xml.dom.NotFoundErr()
+ index = self._index(refChild)
+ self._index_cache = index + 1
 if newChild.nodeType in _nodeTypes_with_children:
 _clear_id_cache(self)
 self.childNodes.insert(index, newChild)
@@ -139,10 +150,7 @@ class Node(xml.dom.Node):
 return
 if newChild.parentNode is not None:
 newChild.parentNode.removeChild(newChild)
- try:
- index = self.childNodes.index(oldChild)
- except ValueError:
- raise xml.dom.NotFoundErr()
+ self._index_cache = index = self._index(oldChild)
 self.childNodes[index] = newChild
 newChild.parentNode = self
 oldChild.parentNode = None
@@ -661,7 +669,7 @@ class TypeInfo(object):
 class Element(Node):
 __slots__=('ownerDocument', 'parentNode', 'tagName', 'nodeName', 'prefix',
 'namespaceURI', '_localName', 'childNodes', '_attrs', '_attrsNS',
- 'nextSibling', 'previousSibling')
+ 'nextSibling', 'previousSibling', '_index_cache')
 nodeType = Node.ELEMENT_NODE
 nodeValue = None
 schemaType = _no_type
</div><div class="naked_ctrl">
<form action="/index.cgi/contrast" method="get" name="gate">
<p><a href="http://altstyle.alfasado.net">AltStyle</a> によって変換されたページ <a href="https://bugs.python.org/file43445/minidom.insertBefore2.patch">(-&gt;オリジナル)</a>
/ <label>アドレス: <input type="text" name="naked_post_url" value="https://bugs.python.org/file43445/minidom.insertBefore2.patch" size="22" /></label> <label>モード: <select name="naked_post_mode">
<option value="default">デフォルト</option>
<option value="speech">音声ブラウザ</option>
<option value="ruby">ルビ付き</option>
<option value="contrast" selected="selected">配色反転</option>
<option value="larger-text">文字拡大</option>
<option value="mobile">モバイル</option>
</select>
<input type="submit" value="表示" />
</p>
</form>
</div>