Python (DAY6)-Functions

Why do I have a function?
Without differentiating the code of all functions together, the question 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

Let's take a look at an example.

"' ************************************hello world************************************" def print_tag (Tag,count , Line_num): For    I in range (line_num):        print (Tag*count) def print_msg (msg): #msg = ' Hello World '    print (msg) Print_tag (' * ', 20,3) print_msg (' Hello World ') print_tag (' * ', 20, 3)

　　

1. Definition phase

def foo ():     print (' from foo ')     bra () def bra ():     print (' from bra ')

　

def func ():  #语法没问题, logic is problematic, referencing a non-existent variable name     ADFKGJKLGNLFIJG

　　

2. Call Stage

Foo () #执行函数语句形式

================================

Res=foo () #执行函数表达式形式
Print (RES)

3. Definition phase: Only the syntax is detected and no code is executed

def func ():    if 1>2       print (' Hahahaha ')

4, three forms of the definition function

No parameter function

def func ():

Pass

Parameter function

def func (x):

Print (x)

Null function

def func ()

Pass

Use of functions: first defined, then called

How to define three forms of function definition function
1. Define the parameterless function: the execution of a function is not dependent on the parameters passed in by the caller, and it needs to be defined as an parameterless function.

Def print_tag ():     print (' ************************* ') Print_tag ()

2. Define parameters: The execution of a function needs to be defined as an argument function when it relies on the arguments passed in by the caller to execute

def func (X,y,*args):     print (x, y)     print (args) func (1,2,3,4,5,6)

def max2 (x, y):     if x > y:         return x     else:         return y res=10*max2 (20,2)    #取大值乘10 Print (res)

　　

def max2 (x, y):    if x > y: #如果x值比y大        return x #返回x值给函数max2    else:        return y #否则返回y值 #11,23,100res=m Ax2 (Max2 (11,23), max), value of #比较x, Y, large value then compare print (RES)

　　

3 Define an empty function:

#3 defining an empty function: The function body is pass# def func (x, Y, z): #     Pass

　

def auth ():    ' user authentication ' '    passdef Get (): '    download file ' '    passdef put (): ' '    upload file    ' Passdef Check_hash ():    ' Check file hash value '    pass

Summarize

The use of the function must follow: the principle of first defining after use

The definition of a function is similar to the definition of a variable, and it is equivalent to referencing a non-existent variable name if it is not directly referenced without defining the function beforehand.

Add: no return in function returns the value of None by default

Contains multiple values, default recognition return value Narimoto group format

Return value: can return any type

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

Python (DAY6)-Functions