title: Convert a Python int into a big-endian string of bytes
body: <p>I have a non-negative int and I would like to efficiently convert it to a big-endian string containing the same data.  For example, the int 1245427 (which is 0x1300F3) should result in a string of length 3 containing three characters whose byte values are 0x13, 0x00, and 0xf3.</p>
  
  <p>My ints are on the scale of 35 (base-10) digits.</p>
  
  <p>How do I do this? </p>