def params(f):
    """
    Read header parameters like ## key=value into a dictionary
    :param f: file handler
    :return: {key: value}
    """
    params = {}
    pos = f.tell()
    line = f.readline()
    while line.startswith('#') or line == '\n':
        if line.startswith('##'):
            line = line[2:].rstrip('\n')
            try:
                idx = line.index('=')
                key = line[0:idx].lstrip()
                value = line[idx + 1:]
                params[key] = value
            except:
                pass
        pos = f.tell()
        line = f.readline()
    f.seek(pos)
    return params
