diff --git a/Lib/xml/dom/domreg.py b/Lib/xml/dom/domreg.py
index f653563..67e0104 100644
--- a/Lib/xml/dom/domreg.py
+++ b/Lib/xml/dom/domreg.py
@@ -62,7 +62,7 @@
 
     # User did not specify a name, try implementations in arbitrary
     # order, returning the one that has the required features
-    if isinstance(features, StringTypes):
+    if isinstance(features, str):
         features = _parse_feature_string(features)
     for creator in registered.values():
         dom = creator()
diff --git a/Lib/xml/dom/expatbuilder.py b/Lib/xml/dom/expatbuilder.py
index fdb5598..a5354b9 100644
--- a/Lib/xml/dom/expatbuilder.py
+++ b/Lib/xml/dom/expatbuilder.py
@@ -918,7 +918,7 @@
     else:
         builder = ExpatBuilder()
 
-    if isinstance(file, StringTypes):
+    if isinstance(file, str):
         fp = open(file, 'rb')
         try:
             result = builder.parseFile(fp)
@@ -952,7 +952,7 @@
     else:
         builder = FragmentBuilder(context)
 
-    if isinstance(file, StringTypes):
+    if isinstance(file, str):
         fp = open(file, 'rb')
         try:
             result = builder.parseFile(fp)
diff --git a/Lib/xml/dom/minidom.py b/Lib/xml/dom/minidom.py
index 1b857a2..3087a5c 100644
--- a/Lib/xml/dom/minidom.py
+++ b/Lib/xml/dom/minidom.py
@@ -498,7 +498,7 @@
         return L
 
     def __contains__(self, key):
-        if isinstance(key, StringTypes):
+        if isinstance(key, str):
             return key in self._attrs
         else:
             return key in self._attrsNS
@@ -531,7 +531,7 @@
 
     # same as set
     def __setitem__(self, attname, value):
-        if isinstance(value, StringTypes):
+        if isinstance(value, str):
             try:
                 node = self._attrs[attname]
             except KeyError:
@@ -1606,7 +1606,7 @@
         return e
 
     def createTextNode(self, data):
-        if not isinstance(data, StringTypes):
+        if not isinstance(data, str):
             raise TypeError("node contents must be a string")
         t = Text()
         t.data = data
@@ -1614,7 +1614,7 @@
         return t
 
     def createCDATASection(self, data):
-        if not isinstance(data, StringTypes):
+        if not isinstance(data, str):
             raise TypeError("node contents must be a string")
         c = CDATASection()
         c.data = data
@@ -1927,7 +1927,7 @@
 
 def getDOMImplementation(features=None):
     if features:
-        if isinstance(features, StringTypes):
+        if isinstance(features, str):
             features = domreg._parse_feature_string(features)
         for f, v in features:
             if not Document.implementation.hasFeature(f, v):