text: #!/usr/bin/env python
  
  import hashlib
  import argparse
  
  
  def fast_hash(infile):
      """
      Calculate a sha256 hash of the first MB of a file and every 512MB offset
      """
  
      m = hashlib.sha256()
      with open(infile, 'rb', 1024 * 1024) as f:
          l = f.read(1024 * 1024)
          while (len(l) > 0):
              m.update(l)
              f.seek(1024 * 1024 * (512 - 1), 1)
              l = f.read(1024 * 1024)
      return m.hexdigest()
  
  
  if __name__ == '__main__':
      parser = argparse.ArgumentParser(description='Calculate file hash')
      parser.add_argument('infile', nargs=1, type=str)
  
      args = parser.parse_args()
      infile = args.infile[0]
  
      print fast_hash(infile)
  