def get_function(available, name):
    """Look up a function by name.

    Args:
        available (dict): name-to-function dictionary of allowed processors.
        func_name (str): name of function to run.

    Returns:
        callable: the desired function.

    Raises:
        AssertionError: if the desired function isn't available.
    """
    assert name in available
    return available[name]