Index: C:/afa/python/py3k/Lib/io.py
===================================================================
--- C:/afa/python/py3k/Lib/io.py	(revision 67577)
+++ C:/afa/python/py3k/Lib/io.py	(working copy)
@@ -684,6 +685,10 @@
             b[:n] = array.array('b', data)
         return n
 
+    def read1(self, n: int = None) -> bytes:
+        """Reads up to n bytes, with at most one read() system call."""
+        self._unsupported("read1")
+
     def write(self, b: bytes) -> int:
         """Write the given buffer to the IO stream.