Index: Lib/io.py
===================================================================
--- Lib/io.py	(revision 66050)
+++ Lib/io.py	(working copy)
@@ -509,6 +509,8 @@
                 return 1
         if limit is None:
             limit = -1
+        if not isinstance(limit, int):
+            raise TypeError("limit must be an integer")
         res = bytearray()
         while limit < 0 or len(res) < limit:
             b = self.read(nreadahead())
@@ -1743,6 +1745,8 @@
             raise ValueError("read from closed file")
         if limit is None:
             limit = -1
+        if not isinstance(limit, int):
+            raise TypeError("limit must be an integer")
 
         # Grab all the decoded text (we will rewind any extra bits later).
         line = self._get_decoded_chars()
@@ -2042,6 +2046,8 @@
                 raise ValueError("read from closed file")
             if limit is None:
                 limit = -1
+            if not isinstance(limit, int):
+                raise TypeError("limit must be an integer")
             if limit >= 0:
                 # XXX: Hack to support limit argument, for backwards
                 # XXX  compatibility