Python basic-------functions

Why do I have a function?
Add the code of all functions without distinction

The problem is:
Poor code readability
Code redundancy
Code can be extended to poor

How to solve?
A function is a tool, the process of preparing a tool beforehand is to define a function, and to refer to it is a function call

Conclusion: The function must be used: defined first, then called

Two: Classification of functions

1. Built-in function: built-in
2. Custom functions:
def function name (parameter 1, parameter 2, ...):
"' Notes '
function body

Three: return value of function

Return value: can return any type
No return:none.
Return Value:value
Return VAL1,VAL2,VAL3:(Val1,val2,val3)

Return effect: Only one value can be returned, terminating the execution of the function

Four: use of function parameters

EF Fuck ():
# if 2>1
# Print (2)
# #定义阶段只检查代码的语法不会执行代码, so there's an error inside the function! 
#
# def fuck ():
# AAAAAAAAAAAAAAAAAAAAAAAAAAAAA
# #虽然语法没错误但是逻辑有问题, referencing a nonexistent variable name. 
# #定义的阶段
# def fuck ():
# print (' Fuck1 ')
# def FUCK1 ():
# print (Fuck ())
# fuck () #调用的阶段
# The Call of the function follows the rule (called) that is defined after it is used! 
# def Fuck2 ():
# return #返回值 can return more than one value returned by default as a tuple can only return one value at a time, and will terminate the execution of the function, so put with the last! 
#返回类型的值, no return will default to none
# def FUCK3 ():
# return ' A ', ' B ', ' C '
# B=FUCK3 ()
# print (b)
# def fuck3 (x, y): #形参, parameters defined by location! Follow the parameters that must be passed in, one more no, one less! 
# Print (' x ', ' y ')
#
# Fuck3 #位置实参, by location-defined arguments! You must first follow the rules of formal parameters! And according to the position and parameter one by one corresponding! 
# Fuck3 (x=1,y=2) #关键字实参, corresponding formal parameters according to the keyword! You must first follow the rules of formal parameters! Match names to formal parameters
# Fuck3 (1,y=2) #混合型实参 (both positional arguments and key glyph parameters!) First, you must follow the rules of formal parameters! and follow the positional arguments must precede the keyword arguments

#可变长参数: The number of arguments in the argument is not fixed! 
#
#
# def FUCK4 (x,y,*mage): #用 * To handle variable-length position real arguments extra arguments are in the form of tuples and assigned to mage variables! * Take it apart for the position parameter encountered! 
# Print (x,y,mage)
# Fuck4 (1,2,3,4,5,6,7,8)
# def FUCK5 (x,y,**kmages): #用 * * to handle variable-length keywords real arguments extra arguments in the form of a dictionary and assign values to the Kmages variable! 
# Print (x,y,kmages)
# FUCK5 (x=1,y=2,z=12,ag=123)
Default parameters
The function defines the parameter by default when it is defined
def cout (a=1): #这个a =1 is the default function

#默认参数需要注意的问题一: Must be placed behind the position parameter
#默认参数需要注意的问题二: Default parameters are typically defined as immutable types
#默认参数需要注意的问题三: Default parameters are assigned only once in the definition phase

#命名关键字参数: Parameters defined in the *, such parameters, must be passed the value, and the truth must be in the form of a keyword to pass the value

# def register (*args,name= ' Egon ', age):
# print (args)
# print (name)
# print (age)
#
# Register (name= ' Egon ', age=18)
# Register (1,2,2,3,age=10

V: nested Use of functions

Nested calls to functions
#
# def max2 (x, y):
# if x > y:
# return X
# Else:
# return Y
#
# def max4 (a,b,c,d):
# RES1=MAX2 (A, b) #23
# RES2=MAX2 (res1,c) #23
# RES3=MAX2 (res2,d) #31
# return Res3
#
#
# Print (max4 (11,23,-7,31))

#函数的嵌套定义
Def f1 ():
def f2 ():
Def f3 ():
Print (' from F3 ')
Print (' from F2 ')
F3 ()
Print (' from F1 ')
F2 ()
# Print (F1)
F1 ()

In the function definition phase, the function is defined in the inner layer.

VI: Function Object

#函数是第一类对象: Refers to a function that can be passed as data

def func ():
Print (' from Func ')

#可被引用
# F=func

#可以当做函数的参数
# def func ():
# print (' from Func ')
# def foo (x):
# Print (x)
# x ()
#
# foo (func)

#可以当做函数的返回值
# def foo ():
# print (' from foo ')
# def bar ():
# return Foo
# F=bar ()
# print (f)
# Print (foo)

# x=0
# def F1 ():
# x=1
# def F2 ():
# # X=2
# Print (x)
# return F2
# F=F1 ()
# # print (f)
# f ()

#可以当做容器类型的元素
# DEF select ():
# print (' Select function ')
#
# func_dic={
# ' SELECT ': SELECT,
# }
#
# # Print (func_dic[' select ')
# func_dic[' select '] ()

Seven: Namespaces and scopes

#名字空间: Holds the binding relationship of the name to the value

#名称空间分为三种

#内置名称空间: The Python interpreter comes with its own name, and the Python interpreter starts to generate

#全局名称空间: The name of the file-level definition is stored with the global namespace, which is generated when the Python file executes

# x=1
# def func ():
# Pass
#
# class Foo:
# Pass
#
# import OS
#
# if 1 > 2:
# y=3

#局部名称空间: Defines the name inside the function, the local namespace only takes effect when the function is called, and the function call ends
# def func (x, y): #x =1,y=2
# z=3

# func ()

#三者的加载顺序: Local namespaces, global namespaces, built-in namespaces

#取值: Built-in namespaces, global namespaces, local namespaces

# # MAX=10
# def func (): #x =1
# # MAX=20
# Print (max)
#
#
# func ()

# max=10
#
# def func (): #x =1
# max=20
# # print (max)
# func ()
#
#
# Print (max)
#

# # X=0
# def F1 ():
# # X=1
# def F2 ():
# # X=2
# def f3 ():
# # X=3
# Print (x)
# F3 ()
# F2 ()
#
# F1 ()

#作用域: Scope of action
#全局作用域: The name of the built-in namespace and the global namespace belong to the global scope,
# can be referenced anywhere in the entire file, valid globally
#局部作用域: The name of the local namespace belongs to the local scope,
#只在函数内部可以被引用, partially effective

# x=1
# def foo ():
# def F2 ():
# Print (x)
# F2 ()
# def bar ():
# Print (x)
#
# foo ()
# Bar ()

# def F1 ():
# x=1
# def F2 (): #f2 =value
# # X=2
# Print (x)
# F2 ()
# F1 ()

X=1
def func ():
x=2
Def f1 ():p
# Print (Dir (Globals () [' __builtins__ ']) #全局作用域name
# print (Locals ()) #局部作用域name

Func ()

Print (Globals () is locals ())

#取值查找顺序 Local Scope-----> global scope

Python basic-------functions