title: python: quickest way to split a file into two files randomly
body: <p>python: what is the quickest way to split a file into two files, each file having half of the number of lines in the original file, such that the lines in each of the two files are random?</p>
  
  <p>for example: if the file is
  1
  2
  3
  4
  5
  6
  7
  8
  9
  10</p>
  
  <p>it could be split into:</p>
  
  <p>3
  2
  10
  9
  1</p>
  
  <p>4
  6
  8
  5
  7</p>