python3-day4-python函数

Posted 2020-08-17

一、函数特性：
减少重复代码
使程序变得可扩展
使程序变得易扩展

定义语法：

def sayhi():
    print("hello")
    return
sayhi()

def sayhi(name):
    print("hello %s" % name)
    return
sayhi("alex")

二、函数参数

1、关键字参数

def sayhi():
    print("hello")
    return
sayhi()

def sayhi(name):
    print("hello %s" % name)
    return
sayhi("alex")

2、默认参数

def sayhi(name,age,job="IT"):
    print("hello %s %s %s" % name,age,job)
    return
sayhi(22,name="alex")

3、位置参数

def sayhi(name,age,job="IT"):
    print("hello %s %s %s" % name,age,job)
    return
sayhi(22,name="alex")

4、非固定参数：arge:*元祖，kargs:**字典   ，a=1  是字典，   单纯的字符串为元祖

def sayhi(name,age,job="IT",*arge,*kwargs*):
    print("hello %s %s %s" % name,age,job)
    print("other arguments:",arge.kargws)
    return
sayhi(22,name="alex")

三、函数变量

1、局部变量：
只在函数内部生效

def sayhi(name,age,job="IT",*arge,*kwargs*):
    print("hello %s %s %s" % name,age,job)
    print("other arguments:",arge.kargws)
    a=123#局部变量
    return
sayhi(22,name="alex")

 

2、返回值：
　　1、返回值：一旦函数经过调用并开始执行，那函数外部的程序就没有办法在控制函数的执行过程，
           　　此时外部程序只能等待函数执行结果，因为外部程序要根据执行结果来决定下一步怎么走，
           　　这个执行结果就是以return的形式返回给外部。
　　2、return代表着一个函数的结束。
　　3、return可以返回任意数据类型。
　　4、return对于用户来讲，可以返回多个任意数量的值，对于python来讲，函数只能返回一个值，多个值会转成元祖(1,2,3,4,5)


3、嵌套函数：

def sayhi(name,age):
    print("hello %s %s" % name,age)
    def sayhi2():
        print("caocao")
    sayhi2()
sayhi()

4、递归：
　　特性：
　　1、必须有一个明确的结束条件
　　2、每次进入更深一层递归时，为题规模相比上次递归都应相应减少
　　3、递归效率不高，递归层次过多会导致栈溢出

5、匿名函数：

def calc(n):
    return n*n
calc2=lambda x:x*x #匿名函数
print(calc(8))

map  把列表的值带入函数进行运算

 

6、三元运算：a=4 b=5

d=a if a>10 else b
if a>10 :
    d=a
else:
    d=b
d=5

 

7、高阶函数：
变量可以指向函数，在函数中调用变量就等于调用函数，这种方法就叫高阶函数
abs：求绝对值

8、内置函数：
1）chr(98) 打印数字对应的assic码
2）ord(a)  打印字母对应的assic码

3）

d=a if a>10 else b
if a>10 :
    d=a
else:
    d=b
d=5

 

4)eval("4+4")#做简单运算

5)dict()字典
6)dir()显示调用方法
7）divmod(10,2)返回商和余
8）filter(lambda x:x>5,range(10)) 过滤满足条件的值
9）globals()以字典的形式打印当前内存中所有的全局变量
10）locals()以字典的形式打印当前内存中的所有局部变量（在函数中）
11）hex()求16进制  0x表示
12）id()求内存地址
13）max()求列表中最大值
14）min()求最小值
15）oct()求8进制  0o表示
16)pow()求x**y幂
17)reversed(data)#反转列表，字符串
18）round((10.26,1))四舍五入
19)set(data),将列表转换成集合
20）slice  等于切片
    pattern= slice(3,8,2)
21）sorted()按照assic对字符串进行排序
22）sum()列表求和
23）vars()跟globals一样
24）zip()#拉链作用，两个列表一一对应
    a=[1,3,5,7]
    b=[2,4,6,8]
    for i in zip(a,b):
        print(i)
四、应用实例：

现需要对这个员工信息文件，实现增删改查操作

1. 可进行模糊查询，语法至少支持下面3种:
   1. 　　select name,age from staff_table where age > 22
   2. 　　select  * from staff_table where dept = "IT"
   3.       select  * from staff_table where enroll_date like "2013"
   4. 查到的信息，打印后，最后面还要显示查到的条数 
2. 可创建新员工纪录，以phone做唯一键，staff_id需自增
3. 可删除指定员工信息纪录，输入员工id，即可删除
4. 可修改员工信息，语法如下:
5. 　　UPDATE staff_table SET dept="Market" WHERE where dept = "IT"

 
文件信息如下：

 

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# user:slim_liu
#date:2016-10-31
def select(user_input):
    id = user.index("where") + 1
    where = user[id:]  # 查询的条件
    sel = user.index("select") + 1
    fro = user.index("from")
    sele = user[sel:fro]  # 查询的内容
    ste = ‘‘.join(sele)
    set = ste.split(",")
    inde = []
    count = 0
    tiaojian = where[0] + " " + where[1] + " " + where[2]
    if where[1] == "=":
        tiaojian = tiaojian.replace("=", "==")
    if "*" not in ste:
        for y in set:
            inde.extend(str(lie.index(y)))
    if "like" not in where:
        for i in f:
            line = i.strip().split(",")
            staff_id = int(line[0])
            name = line[1]
            age = int(line[2])
            phone = str(line[3])
            dept = str(line[4])
            enroll_date = str(line[5])
            if eval(tiaojian):
                for x in set:
                    if x in lie:
                        print(line[lie.index(x)], line[int(inde[1])])
                        count += 1
                        break
                    else:
                        print(line)
                    count += 1
        print("共匹配到", count, "条数据")
    else:
        for i in f:
            line = i.strip().split(",")
            staff_id = int(line[0])
            name = line[1]
            age = int(line[2])
            phone = str(line[3])
            dept = str(line[4])
            enroll_date = str(line[5])
            if "like" in where:
                if str(where[2]).strip(‘‘‘"‘‘‘) in enroll_date:
                    print(line)
                else:
                    continue
            count += 1
        print("共匹配到", count, "条数据")

def update(user_input):
    id = user.index("where") + 1
    where = user[id:]  # 修改后的内容
    sel = user.index("set") + 1
    fro = user.index("where")
    sele = user[sel:fro]  # 被修改的内容
    # ste = ‘‘.join(sele)
    # set = ste.split(",")
    mubiao = where[0] + " " + where[1] + " " + where[2]
    tiaojian = sele[0] + " " + sele[1] + " " + sele[2]
    if where[1] == "=":
        tiaojian = tiaojian.replace("=", "==")
    if sele[1] == "=":
        mubiao = mubiao.replace("=", "==")
    k = open("user1", "w+", encoding="utf-8")
    for i in f:
        line = i.strip().split(",")
        staff_id = int(line[0])
        name = line[1]
        age = int(line[2])
        phone = str(line[3])
        dept = str(line[4])
        enroll_date = str(line[5])
        if eval(tiaojian):
            i = i.replace(str(sele[2]).strip(‘‘‘"‘‘‘), str(where[2].strip(‘‘‘"‘‘‘)))
            print(i.strip(), file=k)
            print("信息更新成功：", i.strip())
        else:
            print(line[0] + "," + line[1] + "," + line[2] + "," + line[3] + "," + line[4] + "," + line[5] + ",", file=k)

    k.close()
    j = open("user1", encoding="utf-8")
    k = open("user", "w+", encoding="utf-8")
    for i in j:
        print(i.strip(), file=k)
    k.close()

def insert(user_input):
    ID = 1
    phone_list = []
    t = open("user", "a+", encoding="utf-8")
    id = user.index("values") + 1
    where = user[id:]  # 插入的值
    le = len(where)
    print(le)
    if le == 4:
        ste = ‘‘.join(where)
        set = ste.strip(‘‘‘)"("‘‘‘).split(" ")
        set2 = str(set[0]).split(",")
        for y in f:
            ID += 1
            phon = y.strip().split(",")
            phone_list.append(phon[3])
        if set2[2].strip("""‘""") in phone_list:
            print("手机号码已存在，添加失败！")
        else:
            print(str(ID) + "," + set2[0].strip("""‘""") + "," + set2[1].strip("""‘""") + "," + set2[2].strip(
                """‘""") + "," + set2[3].strip("""‘""") + "," + set2[4].strip("""‘"""), file=t)
            print("添加成功，本次添加1条")
            print(str(ID) + "," + set2[0].strip("""‘""") + "," + set2[1].strip("""‘""") + "," + set2[2].strip(
                """‘""") + "," + set2[3].strip("""‘""") + "," + set2[4].strip("""‘"""))
        t.close()
    else:
        print("您输入的格式有误,例:[name", "age", "phone", "dept", "enroll_date]，请重新输入：")

def delete(user_input):
    ID = 0
    id = user.index("where") + 1
    where = user[id:]  # 删除的条件
    tiaojian = where[0] + " " + where[1] + " " + where[2]
    if where[1] == "=":
        tiaojian = tiaojian.replace("=", "==")
    r = open("user1", "w+", encoding="utf-8")
    for i in f:
        ID += 1
        line = i.strip().split(",")
        staff_id = int(line[0])
        if eval(tiaojian):
            print("删除成功：",line)
            line.clear()
        else:
            print(line[0] + "," + line[1] + "," + line[2] + "," + line[3] + "," + line[4] + "," + line[5] + ",", file=r)
    r.close()
    j = open("user1", encoding="utf-8")
    k = open("user", "w+", encoding="utf-8")
    id2 = 0
    for i in j:
        id2 += 1
        e = i.split(",")
        i = i.replace(str(e[0]), str(id2))
        print(i.strip(), file=k)
    k.close()

while True:
    user_input = input("cmbh >>")
    f = open(‘user‘, encoding="utf-8")
    lie = ["staff_id", "name", "age", "phone", "dept", "enroll_date"]
    where = ["staff_id", "name", "age", "phone", "dept", "enroll_date", "=", ">=", "<=", ">", "<", "运维", "IT", "SA","无"]
    user = user_input.split(" ")

    if "select" in user:select(user_input)
    elif "insert" in user:insert(user_input)
    elif "delete" in user:delete(user_input)
    elif "update" in user:update(user_input)
    elif "quit" in user or "exit" in user:exit()
    else:print("您的输入有误，请从新输入：")