def dict_to_kwds(dct, kwdstr):
    """ convert a dictionary to a string of keywords

    Parameters
    ----------
    dct : dict
    kwdstr: str
        additional keyword strings

    Examples
    --------
    >>> dict_to_kwds({"a":1,"c":3},'a=1,b=2')
    'a=1,c=3,b=2,'

    """
    string = ''
    for key in sorted(dct.keys()):
        string += '{0}={1},'.format(key, dct[key])
    for kwd in kwdstr.split(","):
        if not kwd.split('=')[0] + '=' in string:
            string += kwd + ','
    return string