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 Function creation ：
def sum(a,b):
    c =a+b
    return print(c)

 Function call ：
sum(10,20)


 Print :
30



-----------------------------------------------

def sum(a,b):
    c =a+b
    return c

print(sum(10,20))

Four . Parameter passing for function calls

Location parameter
- The argument is passed according to the position corresponding to the formal parameter

def calc(a,b):
calc(10,20)  #10 Corresponding a,20 Corresponding b

Keyword arguments
- Pass arguments according to the formal parameter name

def calc(a,b):
calc(b=10,a=20)

5、 ... and . Memory analysis of function calls

''' During a function call , Pass parameters 
 If it's an immutable object , Changes in the function body do not affect the value of the argument 
 If it's a mutable object , Changes in the function body will affect the value of the argument 
'''

n1=11
n2=[22,33,44]
print('n1:',n1)
print('n2:',n2)
print('------------------------------------------------')
def fun(arg1,arg2):
    print('arg1:',arg1)
    print('arg2:',arg2)
    arg1=100
    arg2.append(10)
    print('arg1:',arg1)
    print('arg2:',arg2)
fun(n1,n2)

''' During a function call , Pass parameters 
 If it's an immutable object , Changes in the function body do not affect the value of the argument 
 If it's a mutable object , Changes in the function body will affect the value of the argument 
'''
print('-------------------------------------------------')
print('n1',n1)
print('n2',n2)

 Print ：
n1: 11
n2: [22, 33, 44]
------------------------------------------------
arg1: 11
arg2: [22, 33, 44]
arg1: 100
arg2: [22, 33, 44, 10]
-------------------------------------------------
n1 11
n2 [22, 33, 44, 10]

6、 ... and .return When the function returns multiple values , Result is tuple

def fun2(num):
    odd=[]
    even=[]
    for i in num:
        if i % 2:
            odd.append(i)
        else:
            even.append(i)
    return odd,even

lis=[1,2,3,4,5]
print(fun2(lis))


 Print ：
([1, 3, 5], [2, 4])


---------------------------------------------
def fun2(num):
    odd=[]
    even=[]
    for i in num:
        if i % 2:
            odd.append(i)
        else:
            even.append(i)
    return odd

lis=[1,2,3,4,5]
print(fun2(lis))


 Print ：
[1, 3, 5]

7、 ... and . The return value of the function

If the function does not return a value 【 After the function is executed , There is no need to provide data to the caller 】return You can omit it
The return value of the function , If it is 1 individual , Direct return type
The return value of the function , If more than one , The returned result is a tuple
When a function is defined , Whether to return a value , As the case may be

def fun1():
    print("hello")
fun1()

def fun2():
    return 'hello,word'
print(fun2())

def fun3():
    return 'hell','word'
print(fun3())


 Print ：
hello
hello,word
('hell', 'word')

8、 ... and . Parameter definition of function

1. Function defines default value parameters

When a function is defined , Set default values for parameters , Arguments need to be passed only if they do not match the default values

def fun1(a,b=10):
    print(a,b)

fun1(30)
fun1(30,20)


 Print ：
30 10
30 20

2. Variable number of position parameters *

When defining a function , When the number of location arguments passed may not be determined in advance , Use variable position parameters
Use * Define a variable number of positional parameters
The result is a tuple
When there are multiple parameters , Only the last parameter can be defined *
* and ** When used at the same time , Need to be * before ** After
Each function can only have 1 individual

def fun1(*a):
    print(a)

fun1(10,220,30)

 Print ：
(10, 220, 30)


----------------------------
def fun1(a,*b):
    print(a,b)

fun1(10,220,30)

 Print ：
10 (220, 30)

Reversible call , Turn the elements in the list into arguments and pass them in *list
The elements in the list need to correspond to the number of parameters in the function

def fun1(a,b,c):
    print(a,b,c)

lis=[10,20,30]
fun1(*lis)

 Print ：
10 20 30

3. Variable number of keyword parameters **

When defining a function , When the number of keyword arguments passed cannot be determined in advance , Use variable keyword parameters
Use ** Define a variable number of keyword parameters
The result is a dictionary
When there are multiple parameters , Only the last parameter can be defined **
* and ** When used at the same time , Need to be * before ** After
Each function can only have 1 individual

def fun1(**a):
    print(a)
fun1( Xiao Ming =10, petty thief =20)

 Print ：
{' Xiao Ming ': 10, ' petty thief ': 20}


-----------------------------------

def fun1(a,**b):
    print(a,b)
fun1(10, Xiao Ming =10, petty thief =20)

 Print ：
10 {' Xiao Ming ': 10, ' petty thief ': 20}

------------------------------------

def fun1(*a,**b):  #*  and  **  When used at the same time , Need to be * before  **  After 
    pass


def fun1(**a,*b):  #  Report errors 
    pass

Reversible call , Turn the elements in the list into arguments and pass them in **dict
The elements in the list need to correspond to the number of parameters in the function
key The value needs to be consistent with the parameter name in the function

def fun1(a,b,c):
    print(a,b,c)
dic={"a":50,"b":20,"c":60}

fun1(**dic)


 Print ：
50 20 60

4.def fun1(a,b,*,c,d):# Add * Number , representative * The parameters after No. can only be passed by keywords

def fun1(a,b,*,c,d):
    print(a)
    print(b)
    print(c)
    print(d)
fun1(10,20,c=30,d=40)


 Print ：
10
20
30
40

---------------------------
def fun1(a,b,*,c,**d):  # Sure 
    pass

def fun1(a,b,*,c,*d):  # Can not be 
    pass

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