def query_string(query_dict):
    """Convert a dictionary into a query string URI.

    Args:
        query_dict (dict): Dictionary of query keys and values.

    Returns:
        str: Query string, i.e. ?query1=value&query2=value.
    """
    queries = [
        '{0}={1}'.format(key, query_dict[key]) for key in query_dict.keys()
    ]
    queries_string = '&'.join(queries)
    return '?{0}'.format(queries_string)