diff --git a/src/calibre/gui2/tweak_book/file_list.py b/src/calibre/gui2/tweak_book/file_list.py
index 5f3ac6d36b..1cc0eb4222 100644
--- a/src/calibre/gui2/tweak_book/file_list.py
+++ b/src/calibre/gui2/tweak_book/file_list.py
@@ -1030,6 +1030,6 @@ class FileListWidget(QWidget):
         return self.file_list.current_name
 
     def __getattr__(self, name):
-        if name in self.forwarded_signals:
+        if name in object.__getattribute__(self, 'forwarded_signals'):
             return getattr(self.file_list, name)
         return QWidget.__getattr__(self, name)
diff --git a/src/calibre/gui2/tweak_book/preview.py b/src/calibre/gui2/tweak_book/preview.py
index c2e8633c86..61b443c443 100644
--- a/src/calibre/gui2/tweak_book/preview.py
+++ b/src/calibre/gui2/tweak_book/preview.py
@@ -46,7 +46,10 @@ def get_data(name):
 
 def parse_html(raw):
     root = parse(raw, decoder=lambda x:x.decode('utf-8'), line_numbers=True, linenumber_attribute='data-lnum')
-    return serialize(root, 'text/html').encode('utf-8')
+    ans = serialize(root, 'text/html')
+    if not isinstance(ans, bytes):
+        ans = ans.encode('utf-8')
+    return ans
 
 
 class ParseItem(object):
diff --git a/src/calibre/utils/zipfile.py b/src/calibre/utils/zipfile.py
index 0a9ac3f7da..b1c5bb5281 100644
--- a/src/calibre/utils/zipfile.py
+++ b/src/calibre/utils/zipfile.py
@@ -525,9 +525,9 @@ class ZipExtFile(io.BufferedIOBase):
 
         if self._compress_type == ZIP_DEFLATED:
             self._decompressor = zlib.decompressobj(-15)
-        self._unconsumed = ''
+        self._unconsumed = b''
 
-        self._readbuffer = ''
+        self._readbuffer = b''
         self._offset = 0
 
         self._universal = 'U' in mode
@@ -555,7 +555,7 @@ class ZipExtFile(io.BufferedIOBase):
 
         if not self._universal and limit < 0:
             # Shortcut common case - newline found in buffer.
-            i = self._readbuffer.find('\n', self._offset) + 1
+            i = self._readbuffer.find(b'\n', self._offset) + 1
             if i > 0:
                 line = self._readbuffer[self._offset: i]
                 self._offset = i
@@ -613,7 +613,7 @@ class ZipExtFile(io.BufferedIOBase):
         """Read and return up to n bytes.
         If the argument is omitted, None, or negative, data is read and returned until EOF is reached..
         """
-        buf = ''
+        buf = b''
         if n is None:
             n = -1
         while True: