diff -r c8c9971bdc53 Doc/library/bz2.rst
--- a/Doc/library/bz2.rst	Thu Feb 27 18:48:13 2014 -0500
+++ b/Doc/library/bz2.rst	Thu Mar 06 16:55:26 2014 +0800
@@ -89,11 +89,11 @@
 
    :class:`BZ2File` also provides the following method:
 
-   .. method:: peek([n])
+   .. method:: peek(n=-1)
 
-      Return buffered data without advancing the file position. At least one
-      byte of data will be returned (unless at EOF). The exact number of bytes
-      returned is unspecified.
+      Return n bytes of buffered data without advancing the file position.  If
+      n is omitted or negative, returns all the remaining bytes.  The exact
+      number of bytes returned is unspecified.
 
       .. note:: While calling :meth:`peek` does not change the file position of
          the :class:`BZ2File`, it may change the position of the underlying file
diff -r c8c9971bdc53 Lib/bz2.py
--- a/Lib/bz2.py	Thu Feb 27 18:48:13 2014 -0500
+++ b/Lib/bz2.py	Thu Mar 06 16:55:26 2014 +0800
@@ -265,17 +265,20 @@
         if return_data:
             return b"".join(blocks)
 
-    def peek(self, n=0):
-        """Return buffered data without advancing the file position.
+    def peek(self, n=-1):
+        """Return n bytes of buffered data without advancing the file position.
 
-        Always returns at least one byte of data, unless at EOF.
-        The exact number of bytes returned is unspecified.
+        If n is omitted or negative, returns all the remaining bytes.  The exact
+        number of bytes returned is unspecified.
         """
         with self._lock:
             self._check_can_read()
-            if not self._fill_buffer():
+            if not self._fill_buffer() or n == 0:
                 return b""
-            return self._buffer[self._buffer_offset:]
+            elif n < 0:
+                return self._buffer[self._buffer_offset:]
+            else:
+                return self._buffer[self._buffer_offset:self._buffer_offset+n]
 
     def read(self, size=-1):
         """Read up to size uncompressed bytes from the file.
diff -r c8c9971bdc53 Lib/test/test_bz2.py
--- a/Lib/test/test_bz2.py	Thu Feb 27 18:48:13 2014 -0500
+++ b/Lib/test/test_bz2.py	Thu Mar 06 16:55:26 2014 +0800
@@ -173,6 +173,21 @@
             self.assertNotEqual(len(pdata), 0)
             self.assertTrue(self.TEXT.startswith(pdata))
             self.assertEqual(bz2f.read(), self.TEXT)
+            pdata = bz2f.peek()
+            self.assertEqual(len(pdata), 0)
+
+    def testPeekLimited(self):
+        self.createTempFile()
+        with BZ2File(self.filename) as bz2f:
+            for expected in [b'root:x:0:0:root:/root:/bin/bash\n',
+                             b'bin:x:1:1:bin:/bin:\n']:
+                expected_length = len(expected)
+                pdata = bz2f.peek(n=expected_length)
+                self.assertEqual(pdata, expected)
+                data = bz2f.read(size=expected_length)
+                self.assertEqual(data, expected)
+            pdata = bz2f.peek(n=0)
+            self.assertEqual(pdata, b'')
 
     def testReadInto(self):
         self.createTempFile()
@@ -564,6 +579,21 @@
                 self.assertNotEqual(len(pdata), 0)
                 self.assertTrue(self.TEXT.startswith(pdata))
                 self.assertEqual(bz2f.read(), self.TEXT)
+                pdata = bz2f.peek()
+                self.assertEqual(len(pdata), 0)
+
+    def testPeekBytesIOLimited(self):
+        with BytesIO(self.DATA) as bio:
+            with BZ2File(bio) as bz2f:
+                for expected in [b'root:x:0:0:root:/root:/bin/bash\n',
+                                 b'bin:x:1:1:bin:/bin:\n']:
+                    expected_length = len(expected)
+                    pdata = bz2f.peek(n=expected_length)
+                    self.assertEqual(pdata, expected)
+                    data = bz2f.read(size=expected_length)
+                    self.assertEqual(data, expected)
+                pdata = bz2f.peek(n=0)
+                self.assertEqual(pdata, b'')
 
     def testWriteBytesIO(self):
         with BytesIO() as bio: