# HG changeset patch
# Parent cdc3837cb1fcfc4273b46e84c533ec7e91246b71
Issue 21071: Bytes for Struct format attribute and format string

diff -r cdc3837cb1fc Doc/library/struct.rst
--- a/Doc/library/struct.rst	Tue Dec 16 03:21:54 2014 -0500
+++ b/Doc/library/struct.rst	Tue Dec 16 22:37:18 2014 +0000
@@ -100,7 +100,8 @@
 Format strings are the mechanism used to specify the expected layout when
 packing and unpacking data.  They are built up from :ref:`format-characters`,
 which specify the type of data being packed/unpacked.  In addition, there are
-special characters for controlling the :ref:`struct-alignment`.
+special characters for controlling the :ref:`struct-alignment`.  They are
+normally character strings, but ASCII byte strings are also acceptable.
 
 
 .. _struct-alignment:
@@ -418,7 +419,8 @@
 
    .. attribute:: format
 
-      The format string used to construct this Struct object.
+      The format string used to construct this Struct object, as an ASCII
+      byte string.
 
    .. attribute:: size
 
diff -r cdc3837cb1fc Lib/test/test_struct.py
--- a/Lib/test/test_struct.py	Tue Dec 16 03:21:54 2014 -0500
+++ b/Lib/test/test_struct.py	Tue Dec 16 22:37:18 2014 +0000
@@ -589,6 +589,15 @@
         self.check_sizeof('20p', 1)
         self.check_sizeof('0s', 1)
         self.check_sizeof('0c', 0)
+    
+    def test_format_attr(self):
+        """Make sure the "format" attribute is a byte string"""
+        self.assertEqual(b"x", struct.Struct("x").format)
+
+    def test_bytes_format(self):
+        """Make sure bytes strings are accepted as format strings"""
+        self.assertEqual(b"x", struct.Struct(b"x").format)
+        self.assertEqual(b"\x00", struct.pack(b"x"))
 
 
 class UnpackIteratorTest(unittest.TestCase):
diff -r cdc3837cb1fc Modules/_struct.c
--- a/Modules/_struct.c	Tue Dec 16 03:21:54 2014 -0500
+++ b/Modules/_struct.c	Tue Dec 16 22:37:18 2014 +0000
@@ -1949,7 +1949,8 @@
 #define OFF(x) offsetof(PyStructObject, x)
 
 static PyGetSetDef s_getsetlist[] = {
-    {"format", (getter)s_get_format, (setter)NULL, "struct format string", NULL},
+    {"format", (getter)s_get_format, (setter)NULL,
+        "struct format, as an ASCII byte string", NULL},
     {"size", (getter)s_get_size, (setter)NULL, "struct size in bytes", NULL},
     {NULL} /* sentinel */
 };