def rr(L,a):
    if str(a).isdigit():
        L = str(L)
        print("L is",L)
        k = L.find(".")
        #没有小数点
        if k == -1:
            if a > 0:
                xc = L+"."+"0"*a
            else:
                xc = L
            print("L为整数修正",xc)
        #有小数点
        else:
            #小数点后位数不够添加0
            if len(L[k+1:]) <= a:
                xc = L+"0"*(a-len(L[k+1:]))
                print("L 小数位不够 添加0",xc)
            else:
                #正式进入4舍6入5看
                if int(L[k+a+1]) >= 6:
                    xx = int(L[:k+a+1].replace(".", ""))+1
                    xc = str(xx)[:k]+"."+str(xx)[k:]
                    print("执行6入",xc)
                elif int(L[k+a+1]) <= 4:
                    xc = L[:k+a+1]
                    print("执行4舍",xc)
                else:
                    if L[k+a+2:] != ""and int(L[k+a+2:]) > 0:
                        xx = int(L[:k+a + 1].replace(".", "")) + 1
                        xc = str(xx)[:k] + "." + str(xx)[k:]
                        print("执行5模式后面有数 修约值为",xc)
                    else:
                        if int(L[k+a]) % 2 == 0:
                            xc = L[:k + a + 1]
                            print("执行5前面为偶数舍弃",xc)
                        else:
                            xx = int(L[:k + a + 1].replace(".", "")) + 1
                            xc = str(xx)[:k] + "." + str(xx)[k:]
                            print("执行5前面为奇数 增加",xc)
    else:
       xc = "参数输入有误"
    return xc
#print(rr(69999.9996,3))
#print(rr(69.9994,3))
#print(rr(6999.9995,3))
#print(rr(6999.9945,3))
print(rr(699.994500,3))
#rr(6999.000,3)
#rr(69.994,3)
没有对输入的L 进行处理