Ensure that certain keys are available.
            - exchange
            - period

def price_query_filter(price_query_dict):
    """
        Ensure that certain keys are available.
            - exchange
            - period
    """
    if not isinstance(price_query_dict, dict):
        raise TypeError("dict_list is not a list. Please try again")
    required = ["period", "exchange"]
    pkeys = price_query_dict.keys()
    for r in required:
        if r not in pkeys:
            raise KeyError("An important key is not available {}".format(r))
    return True