def expected_parameters_from_cli(opts):
    """Parses the --expected-parameters arguments from the `plot_posterior`
    option group.

    Parameters
    ----------
    opts : ArgumentParser
        The parsed arguments from the command line.

    Returns
    -------
    dict
        Dictionary of parameter name -> expected value. Only parameters that
        were specified in the --expected-parameters option will be included; if
        no parameters were provided, will return an empty dictionary.
    """
    expected = {}
    for x in opts.expected_parameters:
        x = x.split(':')
        if len(x) != 2:
            raise ValueError(
                'option --expected-paramters not specified correctly; see help'
                )
        expected[x[0]] = float(x[1])
    return expected
