I think the calcsize result is correct here.  With the native struct 
format, padding is included in the struct.

In the second case, there are three bytes of padding after the 'cc' and 
before the 'i'.  This keeps the 'i' aligned on a 4-byte boundary.  If you 
look at the results of struct.pack, you can see the padding explicitly:

Python 2.6.1 (r261:67515, Jul  7 2009, 23:51:51) 
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import struct
>>> struct.pack('ihhi35scci', 123456789, 10000, 10000, 321456789, 
"abcdefghijklmnopqrstuvwxyz123456789", '+', '*', 231456789)
"\x15\xcd[\x07\x10'\x10'\x95\n)\x13abcdefghijklmnopqrstuvwxyz123456789+*\x
00\x00\x00\x15\xc0\xcb\r"