docs: def md5sum(self, f):
          ''' md5sums a file, returning the hex digest
  
              Parameters:
                  - f     filename string
          '''
          m = hashlib.md5()
          fh = open(f, 'r')
          while 1:
              chunk = fh.read(BUF_SIZE)
              if not chunk: break
              m.update(chunk)
          fh.close()
          return m.hexdigest()