python3-day4-python函数
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
- 可进行模糊查询，语法至少支持下面3种:
- select name,age from staff_table where age > 22
- select * from staff_table where dept = "IT"
- select * from staff_table where enroll_date like "2013"
- 查到的信息，打印后，最后面还要显示查到的条数
- 可创建新员工纪录，以phone做唯一键，staff_id需自增
- 可删除指定员工信息纪录，输入员工id，即可删除
- 可修改员工信息，语法如下:
- 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：")
