diff --git a/wx/py/document.py b/wx/py/document.py
index a25a1143..c706e08d 100644
--- a/wx/py/document.py
+++ b/wx/py/document.py
@@ -25,7 +25,7 @@ class Document:
         if self.filepath and os.path.exists(self.filepath):
             f = open(self.filepath, 'rb')
             try:
-                return f.read()
+                return f.read().decode('utf-8')
             finally:
                 f.close()
         else:
@@ -35,6 +35,11 @@ class Document:
         """Write text to file."""
         try:
             f = open(self.filepath, 'wb')
+            try:
+                # Convert from unicode to bytes
+                text = text.encode('utf-8')
+            except AttributeError:
+                pass
             f.write(text)
         finally:
             if f:
diff --git a/wx/py/frame.py b/wx/py/frame.py
index 539110e4..6acbd770 100644
--- a/wx/py/frame.py
+++ b/wx/py/frame.py
@@ -920,7 +920,11 @@ class ShellFrameMixin:
 
     def EditStartupScript(self):
         if os.path.exists(self.startupScript):
-            text = open(self.startupScript, 'U').read()
+            import io
+            # Use newline=None to translate \n \r \r\n to \n on read.  The
+            # old-style mode='U' is deprecated.
+            text = io.open(self.startupScript, 'r',
+                           newline=None, encoding='utf-8').read()
         else:
             text = ''
 
@@ -928,8 +932,8 @@ class ShellFrameMixin:
         if dlg.ShowModal() == wx.ID_OK:
             text = dlg.GetText()
             try:
-                f = open(self.startupScript, 'w')
-                f.write(text)
+                f = open(self.startupScript, 'wb')
+                f.write(text.encode('utf-8'))
                 f.close()
             except:
                 d = wx.MessageDialog(self, "Error saving startup file.",
diff --git a/wx/py/sliceshell.py b/wx/py/sliceshell.py
index 4aa9b7cf..28f4c61c 100755
--- a/wx/py/sliceshell.py
+++ b/wx/py/sliceshell.py
@@ -3715,12 +3715,12 @@ class SlicesShell(editwindow.EditWindow):
 
     def SavePySlicesFile(self,fid):
         addComment=False
-        
+
         def fid_write(s):
             fid.write(s.replace('\r\n', '\n')
                        .replace('\n', os.linesep)
                        .encode('utf-8'))
-        
+
         fid_write(usrBinEnvPythonText)
         fid_write(pyslicesFormatHeaderText[-1])
         for i in range(self.GetLineCount()):
@@ -3734,8 +3734,8 @@ class SlicesShell(editwindow.EditWindow):
                 fid_write(outputStartText)
                 addComment=True
             if addComment:
-                fid.write('#')
-            
+                fid_write(u'#')
+
             fid_write(self.GetLine(i))
 
     # FIX ME!!