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Python学习day11-函数基础函数的定义及定义方式函数的定义函数的定义方式函数的调用及返回值函数的参数猜年龄游戏的函数改编版

Python学习day11-函数基础(1)

函数的定义及定义方式

函数的定义

什么是函数呢？相信大家都接触过别的编程语言，对函数并不陌生，在笔者的理解中，函数就是工具，我们写程序所准备的工具，不管是程序自带的各种函数，还是自己封装的各种函数，都是我们写程序的工具，可以让我们写出来的程序结构更鲜明更简单易懂，修改和扩展的时候也会方便很多。

函数的定义也就相当于提前把工具准备好，随时准备搞出一个不得了的程序，改变世界。

函数的定义方式

函数常用的定义方式有三种，分别是无参函数，有参函数和空函数。下面逐一介绍：

无参函数

顾名思义，无参函数就是没有参数的函数，参数就是定义函数时候后面括号里加的东西，如下：
xxxxxxxxxx

3

1

def func():

2

print('lalalala')

3

func()# 这里括号里都没有参数，故可以被称为无参函数
需要注意的点是，如果定义的时候函数就是无参函数，那么调用的时候也无需传入参数，如果整个函数体并不需要依赖外来的值，自己本身就可以执行和运算，那必须要定义成无参函数。
有参函数

字面意思，括号里有参数，就叫做有参函数。注意的一点是，如果一个函数定义的时候有参数，那么调用的时候就必须传入参数，不然就会报错。而如果整个函数体逻辑需要依赖外部传入的值，必须要定义成有参函数，不然该函数就无法运行。
xxxxxxxxxx

6

1

def mul(x,y):

2

"""乘法"""

3

res = x*y

4

print(res)

5

return res

6

mul(2,3)# 6
空函数

当我们整个程序的结构已经构思之后，若是对某一部分的函数还没有思路，一般可以写一个空函数放在那里，只定义一个函数名，以便于以后回来继续写。例如：
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2

1

def func():

2

pass

函数的调用及返回值

顾名思义，函数的调用其实就是把定义好的函数拿出来用，调用函数就会执行该函数，直到碰到return或者执行完函数体内的所有代码。

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def foo():

    pass

print(foo())

以上函数，如果没有写return返回值，默认返回值是None。

函数的返回值需要注意的大致有几点：

return是一个函数结束的标志，即函数自上而下执行，执行到第一个return就会跳出来，不会执行下面的内容。
return的返回值可以使任意数据类型，字符串，列表，字典，布尔值，都可以
return的返回值没有个数限制，只要用逗号隔开，可以返回任意多个值。但返回值的个数会影响其格式，
- 0个返回值，返回None。
- 一个返回值，维持其原值本身。
- 多个值，返回值是元组。

函数调用的三种形式：

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def mul(x,y):

    """乘法"""

    res = x*y

    print(res)

return res

# 1.

mul(2,3)# 直接调用

# 2.

res = mul(2,3)*100# 可以经过二次计算后赋值调用

# 3.

mul(mul(23,34),4000)# 即可以嵌套调用

函数的参数

形参和实参

1.1 形参

形参就是在定义函数的时候括号内写的参数，叫做形式参数，意思就是，这地方我占了，形参的本质是变量名。
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2

1

def func(x,y):#这里括号里的x，y其实就是形参

2

print(x)
1.2 实参

实参是在调用函数的时候括号内写的值，也就是实际参数，其本质其实就是变量的值。
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1

1

func(1,2)#这里括号里的1,2就是实际参数
位置参数

位置参数同样分为位置形参和位置实参。

其定义类似于形参和实参，不同的是要按照括号内从左到右的顺序依次定义，所以叫位置形参以及位置实参。

需要注意的是，按照位置形参定义的函数，所有的形参都必须被传值，不能多一个或者少一个。
关键字实参

我们调用函数的时候，会见到如下形式：
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1

1

func(y = 2,x = 1)
也就是说关键字实参是类似于字典key:value的形式为指定的参数传值，其特点是可以打破位置的限制，不必在意左右的位置顺序。

要注意的两点是：
1. 位置实参和关键字实参可以一起使用，但是位置实参必须在关键字实参的左边。
2. 位置实参和关键字实参混用的时候，不能对一个形参重复赋值。
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1

1

func(x,y = 2)

2

func(y = 2,x)#报错SyntaxError: positional argument follows keyword argument

3

func(x,x = 1)#报错NameError: name 'x' is not defined
默认形参

从名字就可以看出，默认形参就是在定义阶段就已经被赋值的形参。
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1

1

def func(x,y = 10):

2

print(x)

3

print(y)

4

5

func(2)
由于在定义的时候就已经赋值了，所以其调用的时候可以不用为其赋值。

猜年龄游戏的函数改编版

之前做的猜年龄游戏，整个代码写下来，虽然写的人很清楚逻辑，但是在旁人看来还是会非常复杂，所以在加入函数之后，整个函数体的结构就会十分的清晰，可读性变高，扩展性也会变好，另外又加入了注册和登录函数，代码如下：

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import random

def create_age():

'''生成年龄函数'''

age = random.randint(18, 19)  # 随机一个数字,18-60岁

return age

def open_file():

'''打开文件函数'''

with open('price.txt', 'r', encoding='utf8')as f:  # price.txt右下角为当前文件编码,则encoding后面添加相应编码即可

price_dict = f.read()

price_dict = eval(price_dict)  # type:dict # 获取奖品字典

return price_dict

def select_reward(price_dict = open_file()):

'''选择奖品函数'''

price_self = dict()

# 打印商品

for k, v in price_dict.items():

print(f'奖品编号:{k} {v}')

# 获取奖品的两次循环

for i in range(2):

price_choice = input('请输入你需要的奖品编号:')

if not price_choice.isdigit():

print("恭喜你已经获得一次奖品,奖品为空!并且请输入正确的奖品编号!")

continue

price_choice = int(price_choice)

if price_choice not in price_dict:

print('你想多了吧!')

else:

price_get = price_dict[price_choice]

print(f'恭喜中奖:{price_get}')

if price_self.get(price_get):

price_self[price_get] += 1

else:

price_self[price_get] = 1

print(f'恭喜你获得以下奖品:{price_self}')

def guess_age(age = create_age()):

'''猜年龄函数'''

count = 0  # 计数

while count < 3:

count += 1

inp_age = input('请输入你想要猜的年龄:')

# 判断是否为纯数字

if not inp_age.isdigit():

print('搞事就骂你傻逼')

continue

inp_age = int(inp_age)

# 筛选年龄范围

if inp_age > 60 or inp_age < 18:

print('看好题目,18-60岁,非诚勿扰')

continue

# 核心逻辑

if age == inp_age:

print('猜中了,请选择你的奖品')

select_reward()

break

elif age > inp_age:

print('猜小了')

elif age < inp_age:

print('猜大了')

continue

def login():

'''登录函数'''

username = input('请输入用户名：')

pwd = input('请输入密码：')

with open('user_db.txt','rt',encoding='utf8')as fr:

data = fr.read()

user_list = data.split('\n')

user = f'{username}:{pwd}'

if user in user_list:

print('恭喜您登陆成功')

lo = 1

else:

print('用户名或密码错误')

lo = 0

return lo

def register():

'''注册函数'''

tag = 1

while tag:

username = input('请输入您想注册的用户名：').strip()

pwd = input('请输入您的密码：').strip()

pwd_confirm = input('请确认您的密码：').strip()

if pwd != pwd_confirm:

print('两次密码输入不一致，请重新输入')

continue

100

else:

101

print('注册成功！')

102

tag = 0

103

user = f'{username}:{pwd}'

104

with open('user_db.txt','at',encoding='utf8')as fw:

105

fw.write(user)

106

fw.write('\n')

107

108

109

# game start

110

while True:

111

list = ['1.登录',

112

'2.注册']

113

choice = input(f'请输入您想做的事情：{list}')

114

if choice == '1':

115

lo = login()

116

if lo:

117

create_age()

118

open_file()

119

guess_age()

120

break

121

elif choice == '2':

122

register()

123

continue

124

125

以上每个def都是定义的一个函数，功能分开，逻辑更清楚。