Requirements: Enter the system to display the system function interface, the functions are as follows:
1 , add students
2, delete students
3, modify student information
4, Query student information
5. Display all student information
6. Exit the system
system There are 6 functions in total, users can choose according to their own needs.
Display function interface
User input function serial number
Execute different functions (functions) according to the function number entered by the user
3.1 Define the function
3.2 Call the function
define functionprint_info, responsible for displaying system functions.
def print_info():
print('-' * 20)
print('欢迎登录学员管理系统')
print('1: 添加学员')
print('2: 删除学员')
print('3: 修改学员信息')
print('4: 查询学员信息')
print('5: 显示所有学员信息')
print('6: 退出系统')
print('-' * 20)
print_info()user_num = input('请选择您需要的功能序号：')if user_num == '1':
print('添加学员')
elif user_num == '2':
print('删除学员')
elif user_num == '3':
print('修改学员信息')
elif user_num == '4':
print('查询学员信息')
elif user_num == '5':
print('显示所有学员信息')
elif user_num == '6':
print('退出系统')During work, it needs to be based on the actual situation Requirements for tuning code.
The code for users to select system functions needs to be used repeatedly until the user actively exits the system.
If the user enters a number other than 1-6, the user needs to be prompted.
while True:
# 1. 显示功能界面
print_info()
# 2. 用户选择功能
user_num = input('请选择您需要的功能序号：')
# 3. 根据用户选择，执行不同的功能
if user_num == '1':
print('添加学员')
elif user_num == '2':
print('删除学员')
elif user_num == '3':
print('修改学员信息')
elif user_num == '4':
print('查询学员信息')
elif user_num == '5':
print('显示所有学员信息')
elif user_num == '6':
print('退出系统')
else:
print('输入错误，请重新输入!!!')All functions operate student information, and all student information should be stored in one Global variable , data type is list.
info = []
Requirements analysis
Receive user input of student information, And save
Determine whether to add student information
2.1 If the student name already exists, an error message will be reported
2.2 If the student name does not exist, prepare an empty dictionary and enter the user input The data is appended to the dictionary, and then the dictionary data is appended to the list
Call this function where the corresponding if condition is true
Code implementation
def add_info():
""" 添加学员 """
# 接收用户输入学员信息
new_id = input('请输入学号：')
new_name = input('请输入姓名：')
new_tel = input('请输入手机号：')
# 声明info是全局变量
global info
# 检测用户输入的姓名是否存在，存在则报错提示
for i in info:
if new_name == i['name']:
print('该用户已经存在！')
return
# 如果用户输入的姓名不存在，则添加该学员信息
info_dict = {}
# 将用户输入的数据追加到字典
info_dict['id'] = new_id
info_dict['name'] = new_name
info_dict['tel'] = new_tel
# 将这个学员的字典数据追加到列表
info.append(info_dict)
print(info)Requirements analysis
Press user input Delete the student’s name
The user enters the name of the target student
Check whether this student exists
2.1 If it exists, delete this from the list Data
2.2 If it does not exist, it will prompt "This user does not exist"
Call the function where the corresponding if condition is true
Code implementation
# 删除学员
def del_info():
"""删除学员"""
# 1. 用户输入要删除的学员的姓名
del_name = input('请输入要删除的学员的姓名：')
global info
# 2. 判断学员是否存在:如果输入的姓名存在则删除，否则报错提示
for i in info:
if del_name == i['name']:
info.remove(i)
break
else:
print('该学员不存在')
print(info)Requirements analysis
The user enters the name of the target student
Check whether this student exists
2.1 If it exists, modify the student’s information, such as mobile phone number
2.2 If it does not exist, an error will be reported
Call the function where the corresponding if condition is true
Code implementation
# 修改函数
def modify_info():
"""修改函数"""
# 1. 用户输入要修改的学员的姓名
modify_name = input('请输入要修改的学员的姓名：')
global info
# 2. 判断学员是否存在：如果输入的姓名存在则修改手机号，否则报错提示
for i in info:
if modify_name == i ['name']:
i['tel'] = input('请输入新的手机号：')
break
else:
print('该学员不存在')
print(info)Requirements analysis
The user enters the name of the target student
Check whether the student exists
2.1 If it exists, the student’s information will be displayed
2.2 If it does not exist, an error message will be reported
Call the function where the corresponding if condition is true
Code implementation
# 查询学员
def search_info():
"""查询学员"""
# 1. 输入要查找的学员姓名：
search_name = input('请输入要查找的学员姓名：')
global info
# 2. 判断学员是否存在：如果输入的姓名存在则显示这位学员信息，否则报错提示
for i in info:
if search_name == i['name']:
print('查找到的学员信息如下：----------')
print(f"该学员的学号是{i['id']}, 姓名是{i['name']}, 手机号是{i['tel']}")
break
else:
print('该学员不存在')Requirements analysis
Print all student information
Code
# 显示所有学员信息
def print_all():
""" 显示所有学员信息 """
print('学号\t姓名\t手机号')
for i in info:
print(f'{i["id"]}\t{i["name"]}\t{i["tel"]}')在用户输入功能序号6的时候要退出系统，代码如下：
......
elif user_num == '6':
exit_flag = input('确定要退出吗？yes or no')
if exit_flag == 'yes':
break递归是一种编程思想，应用场景：
在我们日常开发中，如果要遍历一个文件夹下面所有的文件，通常会使用递归来实现；
在后续的算法课程中，很多算法都离不开递归，例如：快速排序。
函数内部自己调用自己
必须有出口
代码
# 3 + 2 + 1 def sum_numbers(num): # 1.如果是1，直接返回1 -- 出口 if num == 1: return 1 # 2.如果不是1，重复执行累加并返回结果 return num + sum_numbers(num-1) sum_result = sum_numbers(3) # 输出结果为6 print(sum_result)
执行结果
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-QST6841K-1597498815746)(03-函数加强.assets/1.png)]
如果一个函数有一个返回值，并且只有一句代码，可以使用 lambda简化。
lambda
注意
lambda表达式的参数可有可无，函数的参数在lambda表达式中完全适用。
lambda表达式能接收任何数量的参数但只能返回一个表达式的值。
# 函数 def fn1(): return 200 print(fn1) print(fn1()) # lambda表达式 fn2 = lambda: 100 print(fn2) print(fn2())
注意：直接打印lambda表达式，输出的是此lambda的内存地址
def add(a, b): return a + b result = add(1, 2) print(result)
思考：需求简单，是否代码多？
fn1 = lambda a, b: a + b print(fn1(1, 2))
fn1 = lambda: 100 print(fn1())
fn1 = lambda a: a
print(fn1('hello world'))fn1 = lambda a, b, c=100: a + b + c print(fn1(10, 20))
fn1 = lambda *args: args print(fn1(10, 20, 30))
注意：这里的可变参数传入到lambda之后，返回值为元组。
fn1 = lambda **kwargs: kwargs print(fn1(name='python', age=20))
fn1 = lambda a, b: a if a > b else b print(fn1(1000, 500))
students = [
{'name': 'TOM', 'age': 20},
{'name': 'ROSE', 'age': 19},
{'name': 'Jack', 'age': 22}
]
# 按name值升序排列
students.sort(key=lambda x: x['name'])
print(students)
# 按name值降序排列
students.sort(key=lambda x: x['name'], reverse=True)
print(students)
# 按age值升序排列
students.sort(key=lambda x: x['age'])
print(students)把函数作为参数传入，这样的函数称为高阶函数，高阶函数是函数式编程的体现。函数式编程就是指这种高度抽象的编程范式。
在Python中，abs()函数可以完成对数字求绝对值计算。
abs(-10) # 10
round()函数可以完成对数字的四舍五入计算。
round(1.2) # 1 round(1.9) # 2
需求：任意两个数字，按照指定要求整理数字后再进行求和计算。
方法1
def add_num(a, b): return abs(a) + abs(b) result = add_num(-1, 2) print(result) # 3
方法2
def sum_num(a, b, f): return f(a) + f(b) result = sum_num(-1, 2, abs) print(result) # 3
注意：两种方法对比之后，发现，方法2的代码会更加简洁，函数灵活性更高。
函数式编程大量使用函数，减少了代码的重复，因此程序比较短，开发速度较快。
map(func, lst)，将传入的函数变量func作用到lst变量的每个元素中，并将结果组成新的列表(Python2)/迭代器(Python3)返回。
需求：计算list1序列中各个数字的2次方。
list1 = [1, 2, 3, 4, 5] def func(x): return x ** 2 result = map(func, list1) print(result) # <map object at 0x0000013769653198> print(list(result)) # [1, 4, 9, 16, 25]
reduce(func，lst)，其中func必须有两个参数。每次func计算的结果继续和序列的下一个元素做累积计算。
注意：reduce()传入的参数func必须接收2个参数。
需求：计算list1序列中各个数字的累加和。
import functools list1 = [1, 2, 3, 4, 5] def func(a, b): return a + b result = functools.reduce(func, list1) print(result) # 15
filter(func, lst)函数用于过滤序列, 过滤掉不符合条件的元素, 返回一个 filter 对象。如果要转换为列表, 可以使用 list() 来转换。
list1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] def func(x): return x % 2 == 0 result = filter(func, list1) print(result) # <filter object at 0x0000017AF9DC3198> print(list(result)) # [2, 4, 6, 8, 10]
递归
函数内部自己调用自己
必须有出口
lambda
语法
lambda 参数列表:
lambda的参数形式
无参数
lambda:
一个参数
lambda 参数:
默认参数
lambda key=value:
不定长位置参数
lambda *args:
不定长关键字参数
lambda **kwargs:
高阶函数
作用：把函数作为参数传入，化简代码
内置高阶函数
map()
reduce()
filter()
The above is the detailed content of How to customize and use functions in Python?. For more information, please follow other related articles on the PHP Chinese website!
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
