def create_constraints(reac_list, lb = 0, up = 0):
    """
    creates a dictionary of constraints ready to be used on other functions that use fba
    :param reac_list: list of str, list of reaction ids to be constrained
    :param lb: int or float, value of the lower bound
    :param up: int or float, value of the upper bound
    :return: dict, a dictionary with reaction ids as keys, and tuples of lower and upper
        bounds as values
    """
    if lb > up:
        raise Exception("Lower bound must be lower than upper bound")
    cons_dic = {}
    for reac in reac_list:
        cons_dic[reac] = (lb, up)
    return cons_dic