Very dumb question

Wed Oct 12 09:39:29 EDT 2005

I have a program with this code fragment:

    print len(data)
    print data[:50]
    raise SystemExit

This prints:

20381
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"

But if I change 50 to 51

    print len(data)
    print data[:51]
    raise SystemExit

then it prints

20381
 !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"

After all, only the last 50 bytes are printed. The string is the same 
(length 20381) in both cases.
Surprisingly, I can print more than 50 characters, this works:

print "012345678901234567890123456789012345678901234567890123456789A"

I'm sure it is my mistake, but I don't know what am I doing wrong. Do 
you have an idea?
Thanks,

   Les