How to create and call functions in Python?-Python Tutorial-php.cn

Create function

The function is created with the def statement. The syntax is as follows:

def 函数名(参数列表):  # 具体情况具体对待，参数可有可无
	"""函数说明文档字符串"""
    函数封装的代码
    ……

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The title line consists of the def keyword, the name of the function, and the set of arguments (if any) forming the

def The remainder of the clause includes an optional but strongly recommended docstring, and Required function body

The naming of function name should comply with the naming rules of identifiers

can be composed of letters, underscores and numbers
cannot start with numbers
cannot have the same name as a keyword

def washing_machine():  # 洗衣机可以帮我们完成
    print("打水")
    print("洗衣服")
    print("甩干")

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Calling a function

Use a pair of parentheses () to call a function. If there are no parentheses, it is just a reference to the function.

Any input parameters All must be placed in brackets

Legend:

How to create and call functions in Python?

Case: Add washing powder

def washing_machine():  # 洗衣机可以帮我们完成
    print("打水")
    print("加洗衣粉！！！")
    print("洗衣服")
    print("甩干")
# 早上洗衣服
washing_machine()
# 中午洗衣服
washing_machine()
# 晚上洗衣服
washing_machine()

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How to create and call functions in Python?

Summary

After defining the function, it only means that this function encapsulates a piece of code
If you do not actively call the function, the function will not actively execute

Thinking

Can I put function call above function definition?

cannot!
Because before using the function name to call the function, you must ensure that Python already knows the existence of the function
Otherwise the console will prompt NameError: name 'menu' is not defined (NameError: the name menu is not defined)

Parameters of function

Formal parameters and actual parameters

##Formal parameters:When defining function , the parameters in parentheses are used to receive parameters. Inside the function is used as a variable
actual parameter : When calling a function, the parameters in parentheses are used to pass data to inside the function

Question

When we want to wash other things, we need to manually change the code inside the method:

def washing_machine():  # 洗衣机可以帮我们完成
    print("打水")
    print("加洗衣粉！！！")
    print("洗床单")  # 洗被套
    print("甩干")

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There are certain changing values inside the function:

def washing_machine():  # 洗衣机可以帮我们完成
    print("打水")
    print("加洗衣粉！！！")
    print("洗衣服")
    print("甩干")
washing_machine()
def washing_machine():  # 洗衣机可以帮我们完成
    print("打水")
    print("加洗衣粉！！！")
    print("洗床单")
    print("甩干")
washing_machine()
......

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Thinking What are the problems?

The function can only process fixed data

How to solve it?

It would be great if the data that needs to be processed can be passed to the inside of the function when calling the function!

Pass parameters

Fill in the parentheses after the function name
Parameters
More Use
, to separate the parameters
When calling a function, the number of actual parameters needs to be consistent with the number of formal parameters, and the actual parameters will be passed to the formal parameters in turn. Parameter

def washing_machine(something):  # 洗衣机可以帮我们完成
    print("打水")
    print("加洗衣粉！！！")
    print("洗" + something)
    print("甩干")
# 洗衣服
washing_machine("衣服")
# 洗床单
washing_machine("床单")

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Legend

How to create and call functions in Python?

def washing_machine(xidiji,something):  # 洗衣机可以帮我们完成
    print("打水")
    print("加" + xidiji)
    print("洗衣服" + something)
    print("甩干")
#早上洗衣服
#按照参数位置顺序传递参数的方式叫做位置传参
#使用洗衣机，执行洗衣机内部的逻辑
washing_machine("洗衣液","衣服")#something = 衣服
#中午洗被罩
washing_machine("洗衣粉","被罩")# something = 被罩
#晚上洗床单
washing_machine("五粮液","床单")# something = 床单

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Function

The

function organizes code blocks with independent functions into a small module and calls the parameters of the
function when needed to increase the versatility of the function and target the same The data processing logic can adapt to more data

1. Inside the function, use the parameters as variables to perform the required data processing

2. Function call When, according to the parameter order defined by the function, pass the data you want to process inside the function through the parameters

Positional parameters

are similar to

shell scripts, program The name and parameters are passed to the python program in the form of positional parameters, using the sys module's argv list to receive

Legend

How to create and call functions in Python?

Default parameters

Default parameters are parameters that declare

Default value. Because a default value is assigned to the parameter, when the function is called It is also allowed not to pass a value to the parameter

The return value of the function

In program development, sometimes, you will want
A function to execute After the end, tell the caller a result so that the caller can perform subsequent processing on the specific result
The return value is the function to complete the work After that, Finally gives the caller a result
在函数中使用 return 关键字可以返回结果
调用函数一方，可以 使用变量 来接收函数的返回结果

案例：计算任意两个数字的和

# 函数的返回值: return, 用于对后续逻辑的处理
# 理解: 把结果揣兜里，后续想干啥干啥，想打印打印，想求和就求和
# 注意:
# a. 函数中如果没有return，那么解释器会自动加一个return None
# b. return表示函数的终止，return后的代码都不会执行
# 1 定义一个函数，计算两个数的和
# 2 计算这两个数的和是不是偶数
def get_sum(x, y=100):  # 默认参数
    he = x + y  # sum = 10 + 20
    return he   # return 30
    print("return表示函数的终止，return后的代码都不会执行")
# 将函数return后的结果赋值给变量dc: dc = sum  ->  dc = 30
dc = get_sum(10, 20)  # x = 10, y = 20
print("dc:", dc)  # 30
dc1 = get_sum(10)  # x = 10, y = 100
print("dc1:", dc1)  # 110
# if dc % 2 == 0:
#     print("偶数")
# else:
#     print("奇数")

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#默认参数
#注意：具有默认值的参数后面不能跟没有默认值的参数
def get_sum(a=20,b=5,c=10):
    he = a + b+ c
    return he
 
dc = get_sum(1,2,3) #a=1 b=2 c=3
print("dc:",dc) # 6
dc1 = get_sum(1,2)  # a=1 b=2 c=10
print("dc1:",dc1) # 13
dc2 = get_sum(1)  # a=1 b=5 c=10
print("dc2:",dc2) # 16
dc3 = get_sum()
print("dc3:",dc3) # 35

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How to create and call functions in Python?

修改菲波那切数列

def new_fib(n=8):
    list01 = [0,1]  #定义列表，指定初始值
    for dc in range(n-2):
        list01.append(list01[-1]+list01[-2])
    return list01
 
dc = new_fib()   #不加参数默认是8
dc1 = new_fib(10)
print("dc:",dc)
print("dc1:",dc1)

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How to create and call functions in Python?

生成随机密码：

#练习：生成随机密码
#创建 randpass.py 脚本，要求如下：
#编写一个能生成8位随机密码的程序
#使用 random 的 choice 函数随机取出字符
#由用户决定密码长度
import random
def new_password():
    n = int(input("密码长度："))
    password = ""
    all = "0123456789zxcvbnmlkjhgfdsaqwertyuiopPOIUYTREWQASDFGHJKLMNBVCXZ" # 0-9 a-z A-Z
    random.choice(all)
    for i in range(n):
        dc = random.choice(all)
        password += dc
    # print("passwd:",password)
    return password
# 调用函数，才能执行函数内部逻辑
dc = new_password()
print("dc:",dc)

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How to create and call functions in Python?

#练习：生成随机密码
#创建 randpass.py 脚本，要求如下：
#编写一个能生成8位随机密码的程序
#使用 random 的 choice 函数随机取出字符
#由用户决定密码长度
import random,string
def new_password():
    n = int(input("密码长度："))
    password = ""
    all = string.ascii_letters + string.digits
    random.choice(all)
    for i in range(n):
        dc = random.choice(all)
        password += dc
    # print("passwd:",password)
    return password
# 调用函数，才能执行函数内部逻辑
dc = new_password()
print("dc:",dc)

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How to create and call functions in Python?

模块基础

定义模块

基本概念

模块是从逻辑上组织python代码的形式
当代码量变得相当大的时候，最好把代码分成一些有组织的代码段，前提是保证它们的 彼此交互
这些代码片段相互间有一定的联系，可能是一个包含数据成员和方法的类，也可能是一组相关但彼此独立的操作函数

导入模块 (import)

使用 import 导入模块
模块属性通过 “模块名.属性” 的方法调用
如果仅需要模块中的某些属性，也可以单独导入

为什么需要导入模块？

可以提升开发效率，简化代码

How to create and call functions in Python?

正确使用

# test.py，将 file_copy.py 放在同级目录下
# 需求：要将/etc/passwd复制到/tmp/passwd
src_path = "/etc/passwd"
dst_path = "/tmp/passwd"
# 如何复制？
# 调用已有模块中的方法
#    - 很推荐，简单粗暴不动脑
#    - 直接使用 file_copy.py的方法即可
 
# 导入方法一：直接导入模块
import file_copy  # 要注意路径问题
file_copy.copy(src_path, dst_path)
 
# 导入方法二：只导入 file_copy 模块的 copy 方法
from file_copy import copy  # 如果相同时导入多个模块 from file_copy import *
copy(src_path, dst_path)
 
# 导入方法四：导入模块起别名 as
import file_copy as fc
fc.copy(src_path, dst_path)

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常用的导入模块的方法

一行指导入一个模块，可以导入多行，例如：import random
只导入模块中的某些方法，例如：from random import choice, randint

模块加载 (load)

一个模块只被 加载一次，无论它被导入多少次
只加载一次可以 阻止多重导入时，代码被多次执行
如果两个文件相互导入，防止了无限的相互加载
模块加载时，顶层代码会自动执行，所以只将函数放入模块的顶层是最好的编程习惯

模块特性及案例

模块特性

模块在被导入时，会先完整的执行一次模块中的 所有程序

案例

# foo.py
print(__name__)
 
# bar.py
import foo  # 导入foo.py，会将 foo.py 中的代码完成的执行一次，所以会执行 foo 中的 print(__name__)

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结果：

# foo.py -> __main__ 当模块文件直接执行时，__name__的值为‘__main__’
# bar.py -> foo 当模块被另一个文件导入时，__name__的值就是该模块的名字

How to create and call functions in Python?

所以我们以后在 Python 模块中执行代码的标准格式：

def test():
    ......
if __name__ == "__main__":
    test()

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