diff -r aaf2ad84ae1c Lib/test/test_mmap.py
--- a/Lib/test/test_mmap.py	Thu Apr 28 14:47:33 2016 -0500
+++ b/Lib/test/test_mmap.py	Fri Apr 29 15:50:05 2016 +0800
@@ -54,6 +54,17 @@
         self.assertRaises(IndexError, m.__getitem__, len(m))
         self.assertRaises(IndexError, m.__setitem__, len(m), b'\0')
 
+        # Iteration returns int instead of bytes
+        for byte in m:
+            self.assertIsInstance(byte, int)
+
+        # Test in operator behaviour
+        self.assertTrue(102 in m)
+        self.assertTrue(b'f' in m)
+        self.assertTrue(b'foo' in m)
+        self.assertRaises(TypeError, lambda: 'foo' in m)
+        self.assertRaises(ValueError, lambda: -1 in m)
+
         # Modify the file's content
         m[0] = b'3'[0]
         m[PAGESIZE +3: PAGESIZE +3+3] = b'bar'
diff -r aaf2ad84ae1c Modules/mmapmodule.c
--- a/Modules/mmapmodule.c	Thu Apr 28 14:47:33 2016 -0500
+++ b/Modules/mmapmodule.c	Fri Apr 29 15:50:05 2016 +0800
@@ -790,7 +790,7 @@
         PyErr_SetString(PyExc_IndexError, "mmap index out of range");
         return NULL;
     }
-    return PyBytes_FromStringAndSize(self->data + i, 1);
+    return PyLong_FromLong(Py_CHARMASK(self->data[i]));
 }
 
 static PyObject *
@@ -866,6 +866,45 @@
 }
 
 static int
+mmap_contains(PyObject *mmap, PyObject *arg)
+{
+    Py_ssize_t ival;
+    mmap_object *self = (mmap_object *)mmap;
+
+    CHECK_VALID(-1);
+    ival = PyNumber_AsSsize_t(arg, PyExc_ValueError);
+    if (ival == -1 && PyErr_Occurred()) {
+        Py_buffer view;
+        Py_ssize_t i, len;
+        const char *p, *end, *needle;
+
+        PyErr_Clear();
+        if (PyObject_GetBuffer(arg, &view, PyBUF_SIMPLE) != 0)
+            return -1;
+
+        len = view.len;
+        needle = view.buf;
+        end = self->data + self->size;
+        for (p = self->data; p + len <= end; ++p) {
+            for (i = 0; i < len && needle[i] == p[i]; ++i)
+                ;
+            if (i == len) {
+                PyBuffer_Release(&view);
+                return 1;
+            }
+        }
+        PyBuffer_Release(&view);
+        return 0;
+    }
+    if (ival < 0 || ival >= 256) {
+        PyErr_SetString(PyExc_ValueError, "byte must be in range(0, 256)");
+        return -1;
+    }
+
+    return memchr(self->data, (int)ival, self->size) != NULL;
+}
+
+static int
 mmap_ass_item(mmap_object *self, Py_ssize_t i, PyObject *v)
 {
     const char *buf;
@@ -991,6 +1030,7 @@
     0,                               /*sq_slice*/
     (ssizeobjargproc)mmap_ass_item,  /*sq_ass_item*/
     0,                               /*sq_ass_slice*/
+    (objobjproc)mmap_contains,       /*sq_contains*/
 };
 
 static PyMappingMethods mmap_as_mapping = {