diff --git a/Lib/poplib.py b/Lib/poplib.py
index 8ad9cb7..1224eac 100644
--- a/Lib/poplib.py
+++ b/Lib/poplib.py
@@ -136,7 +136,7 @@
         # so only possibilities are ...LF, ...CRLF, CR...LF
         if line[-2:] == CRLF:
             return line[:-2], octets
-        if line[0] == CR:
+        if line[:1] == CR:
             return line[1:-1], octets
         return line[:-1], octets
 
diff --git a/Lib/quopri.py b/Lib/quopri.py
index 46c2a4c..cbd979a 100755
--- a/Lib/quopri.py
+++ b/Lib/quopri.py
@@ -145,7 +145,7 @@
                 new = new + c; i = i+1
             elif i+1 == n and not partial:
                 partial = 1; break
-            elif i+1 < n and line[i+1] == ESCAPE:
+            elif i+1 < n and line[i+1:i+2] == ESCAPE:
                 new = new + ESCAPE; i = i+2
             elif i+2 < n and ishex(line[i+1:i+2]) and ishex(line[i+2:i+3]):
                 new = new + bytes((unhex(line[i+1:i+3]),)); i = i+3
diff --git a/Lib/sunau.py b/Lib/sunau.py
index 3c24492..3da41b7 100644
--- a/Lib/sunau.py
+++ b/Lib/sunau.py
@@ -210,12 +210,9 @@
         self._framesize = self._framesize * self._nchannels
         if self._hdr_size > 24:
             self._info = file.read(self._hdr_size - 24)
-            for i in range(len(self._info)):
-                if self._info[i] == b'\0':
-                    self._info = self._info[:i]
-                    break
+            self._info, _, _ = self._info.partition(b'\0')
         else:
-            self._info = ''
+            self._info = b''
         try:
             self._data_pos = file.tell()
         except (AttributeError, OSError):
diff --git a/Lib/test/test_buffer.py b/Lib/test/test_buffer.py
index e84f3e4..aa15377 100644
--- a/Lib/test/test_buffer.py
+++ b/Lib/test/test_buffer.py
@@ -149,15 +149,15 @@
        format character."""
     x = randrange(*fmtdict[mode][char])
     if char == 'c':
-        x = bytes(chr(x), 'latin1')
+        x = bytes([x])
+        if obj == 'numpy' and x == b'\x00':
+            # http://projects.scipy.org/numpy/ticket/1925
+            x = b'\x01'
     if char == '?':
         x = bool(x)
     if char == 'f' or char == 'd':
         x = struct.pack(char, x)
         x = struct.unpack(char, x)[0]
-    if obj == 'numpy' and x == b'\x00':
-        # http://projects.scipy.org/numpy/ticket/1925
-        x = b'\x01'
     return x
 
 def gen_item(fmt, obj):
diff --git a/Lib/test/test_tokenize.py b/Lib/test/test_tokenize.py
index 38611a7..4a8be3b 100644
--- a/Lib/test/test_tokenize.py
+++ b/Lib/test/test_tokenize.py
@@ -1066,7 +1066,7 @@
         encoding = object()
         encoding_used = None
         def mock_detect_encoding(readline):
-            return encoding, ['first', 'second']
+            return encoding, [b'first', b'second']
 
         def mock__tokenize(readline, encoding):
             nonlocal encoding_used
@@ -1085,7 +1085,7 @@
             counter += 1
             if counter == 5:
                 return b''
-            return counter
+            return str(counter).encode()
 
         orig_detect_encoding = tokenize_module.detect_encoding
         orig__tokenize = tokenize_module._tokenize
@@ -1093,7 +1093,8 @@
         tokenize_module._tokenize = mock__tokenize
         try:
             results = tokenize(mock_readline)
-            self.assertEqual(list(results), ['first', 'second', 1, 2, 3, 4])
+            self.assertEqual(list(results),
+                             [b'first', b'second', b'1', b'2', b'3', b'4'])
         finally:
             tokenize_module.detect_encoding = orig_detect_encoding
             tokenize_module._tokenize = orig__tokenize