def _check_file(fname, overwrite):
 if (op.isfile(fname) and (not overwrite)):
  raise IOError(('File %s exists, use --overwrite to overwrite it' % fname))

def _check_file ( fname , overwrite ) : if ( op . isfile ( fname ) and ( not overwrite ) ) : raise IOError ( ( 'File %s exists, use --overwrite to overwrite it' % fname ) )
prevent overwrites .