Null-terminated strings with struct module?

[Roy Smith]

I need to generate packed binary data which includes null-terminated 
strings mixed in with binary numbers.  For example, the Python string 
"foo" needs to become the 4-character binary string "foo\0", just like a 
C string (don't ask, I didn't design the protocol).

What's the best way to do this?  The "s" format specifier in struct 
gives me fixed-length, non-null-terminated strings.  Right now I'm doing:

        s1 = self.directory + "\0"
        s2 = self.fileName + "\0"
        s3 = self.dateString + "\0"
        s4 = self.name + "\0"
        s5 = struct.pack ("!IB", self.id, self.perTargetFlag)
        data = s1 + s2 + s3 + s4 + s5

which is pretty ugly.  Is there a neater way to do this?

I know the string addition isn't the most efficient way to go, but for 
this application, I prefer the clarity and don't mind the minor speed 
hit.