Keep only the slicing under the lock, and test a float size

The size normalisation touches no shared state, so it does not need the lock.

Author: fedonman

Lib/_pyio.py

@@ -1010,9 +1010,10 @@ def peek(self, size=0):
         else:
             size = size_index()
 
+        if size < 1:
+            size = io.DEFAULT_BUFFER_SIZE
+
         with self._lock:
-            if size < 1:
-                size = io.DEFAULT_BUFFER_SIZE
             b = self._buffer[self._pos:self._pos + size]
             return b.take_bytes()
 

Lib/test/test_io/test_memoryio.py

@@ -574,6 +574,7 @@ def test_peek(self):
             self.assertIsInstance(memio.peek(), bytes)
             self.assertIsInstance(memio.peek(1), bytes)
             self.assertEqual(memio.peek(IntLike(3)), buf[:3])
+            self.assertRaises(TypeError, memio.peek, 1.5)
             self.assertEqual(memio.peek(1), buf[:1])
             self.assertEqual(memio.peek(1), buf[:1])
             self.assertEqual(memio.peek(), buf)