python day10 function (second part)

Keywords: Python CentOS git

Summary of 2010.4.10 S21 Day10 Notes

I. Content Review

1. Interview questions are relevant:
  - 1.The difference between py2 and py3
  - 2. Operator calculation: 3 or 9 and 8
  - 3. String inversion
  - 4. The difference between is and===
  - 5.v1 = 1) V2 = 1 V3 = 1,) What's the difference?
    
    v1, v2 are numbers, v3 is tuples
  - 6. Online Operating System: centos
  - 7. List the methods you understand for each data type
  - 8. Deep and shallow copies
  - 9. File operation, how to read large files (such as 50G log files)
    
    v=open(……)
    
    for line in v:
    
    print(line)
    
    v.close()
  - 10. Write in one line: 9*9 multiplication table
  - git process
1. function
  
  The method (data type) is similar to a function, but not a function.
  
  Pass parameters strictly in sequence: position mode
  
  Actual parameters can be of any type
  
  When return has no return value, return None by default
  
  The role of return: 1. Return value 2. Termination function execution
  
  In the internal execution of a function, it terminates when it encounters return
  
  Return can return any type
  
  Special case: return 1,2,'alex'means that the tuple returned is the same as return(1,2,'alex').

II. Today's Contents

1. parameter

1.1 Basic parameter knowledge

The parameters can be any number.

It can be of any type

def func(a1,a2,a3,a4):
  print(a1,a2,a3,a4)

func(2,'name',[1,2,3],False)

1.2 Location parameter (calling function and passing parameter) (execution)

Input parameters strictly in place order when calling/executing functions

def func(a1,a2,a3):
    print(a1,a2,a3)
    
func(66,'alex',3)

1.3 Keyword Reference (Execution)

Keyword parameterization is the use of parameterization in arguments.

def func(a1,a2):
    print(a1,a2)
    
func(a1=22,a2=8)

Keyword input and location reference can be mixed: location input parameters should be placed in front, keyword input should be placed behind, and finally equal to the total number of parameters.

def func(a1,a2,a3):
    print(a1,a2,a3)
    
func(1,2,a3=3)
func(1,a2=2,a3=3)
func(a1=1,a2=2,a3=3)
func(a1=1,2,3)  # It's wrong.

def func(): the custom function open() are python's built-in functions

pass len()

1.4 Default parameter

def func(a1,a2,a3=9,a4=10):   # The default parameters a3=9,a4=10
    print(a1,a2,a3,a4)

func(11,22)       # If the values of A3 and A4 are not passed, then A3 and A4 are equal to the default parameters.
func(11,22,10)
func(11,22,10,100)
func(11,22,10,a4=100)
func(11,22,a3=10,a4=100)
func(11,a2=22,a3=10,a4=100)
func(a1=11,a2=22,a3=10,a4=100)

15 Universal Parameters (for Dispersion)

*args

It can accept any number of position parameters and convert them into tuples.

Call function without*

def func(*args):
  print(*args)

func(1,2)   ==> (1,2)
func(1,2,[12,3,4])   ==> (1,2,[12,3,4])
func((11,22,33))   ==> ((11,22,33))  # The parameter is a tuple, and the print effect is tuple set tuple.

The calling function has*

def func(*args):
  print(*args)

func(*(11,22,33))   ==>(11,22,33)    # * It is used to break up tuples, with each element in the tuple as a parameter.
func(*[11,22,33])   ==>(11,22,33)    # * It can be used to hash lists / tuples / dictionaries / collections, just the internal elements of loops

Reference can only be transmitted by location

def func(*args):
    print(args)

func(1)
func(1,2)   # args=(1, 2)
func((11,22,33,44,55))    # args=((11,22,33,44,55),)
func(*(11,22,33,44,55))   # args=(11,22,33,44,55)

**kwargs

Can accept any number of keyword parameters, and see the parameters into a dictionary

Call function without*

def func(**kwargs):
  print(***kwargs)

func(k=1)    **kwargs = {'k':1}
func(k1=1,k2=3)   **kwargs = {'k1':1,'k2':3}

The calling function has*

def func(**kwargs):
  print(**kwargs)

func(**{'k1':1,'k2':4,'k3':9})   **kwargs = {'k1':1,'k2':4,'k3':9}

Reference can only be transmitted by keywords

* Comprehensive use of args/**kwargs: invincible + invincible=> truly invincible

def func(*args,**kwargs):
    print(args,kwargs)

func(1,2,3,4,5,k1=2,k5=9,k19=999)     *arg = (1,2,3,4,5) **kwargs = {'k1':2,'k5':9,'k19':999}
func(*[1,2,3],k1=2,k5=9,k19=999)      *arg = (1,2,3) **kwargs = {'k1':2,'k5':9,'k19':999}
func(*[1,2,3],**{'k1':1,'k2':3})      *arg = (1,2,3) **kwargs = {'k1':1,'k2':3}
func(111,222,*[1,2,3],k11='alex',**{'k1':1,'k2':3})  
*arg = (111,222,1,2,3)   **kwargs = {'k11':'alex','k1':1,'k2':3}

1.6 Key Points Related to Parameters

Defined function

def func(a1,a2):
  pass

def func(a1,a2=None):  # For default values, the immutable type is written casually, if it is a variable type (pitted).
  pass

def func(*args,**kwargs):
  pass

Calling function

Position parameters are in the first place and keyword parameters are in the second place.

2. scope of action

In the python file:

py file: global scope

Function: Local scope

a = 1
def s1():
    x1 = 666
    print(x1)
    print(a)
    print(b)

b = 2
print(a)
s1()
a = 88888
def s2():
    print(a,b)
    s1()

s2()

Data in each scope can only be invoked by the scope itself. If the data invoked in the scope is not available, the global scope can be invoked.

Global scope can only call Global

Functions in global scope can call each other (calling existing ones), but they cannot call scopes directly in scope.

Conclusion:

1. A function is a scope.

2. Data search rules in scopes: first, find data in their own scopes, they did not go to the "parent" - > "parent" - > until the whole situation, the whole situation without error. (Scope nesting)

Note: What is the value in the parent scope?

x = 10
def func():
    x = 9
    print(x)

func()

Exercises in class

x = 10
def func():
    x = 9
    print(x)
    def x1():
        x = 999
        print(x)

func()



x = 10
def func():
    x = 9
    print(x)
    def x1():
        x = 999
        print(x)
    x1()

func()


x = 10
def func():
    x = 9
    print(x)
    def x1():
        x = 999
        print(x)
    print(x)
    x1()

func()

x = 10
def func():
    x = 8
    print(x)
    def x1():
        x = 999
        print(x)
    x1()
    print(x)

func()


x = 10
def func():
    x = 8
    print(x)
    def x1():
        print(x)
    x1()
    print(x)

func()



x = 10
def func():
    x = 8
    print(x)
    def x1():
        print(x)
    x = 9
    x1()
    x = 10
    print(x)

func()

x = 10
def func():
    x = 8
    print(x)
    def x1():
        print(x)    
    x1()
    x = 9
    x1()
    x = 10
    print(x)

func()

3. Values in the parent can only be found in the child scope, and cannot be reassigned to variables in the parent by default.

No assignment, only internal modification of variable types

# #####################
name = 'oldboy'
def func():
    name = 'alex' # Create another such value in your own scope.
    print(name)
func()
print(name)


# #####################
name = [1,2,43]
def func():
    name.append(999)
    print(name)
func()
print(name)

If you have to assign global variables, you need to add global (mandatory assignment)

#Example 1
name = "Old boy "
def func():
    global name
    name = 'alex'
func()
print name

# Example two
name = ["Old boy",'alex']
def func():
    global name
    name = 'I'
func()
print(name)

# Example three
name = "Old boy"
def func():
    name = 'alex'
    def inner():
        global name
        name = 999
    inner()
    print(name)
func()
print(name)

To assign a parent variable to a nonlocal value, first find the parent variable and then assign it (mandatory assignment)

name = "Old boy"
def func():
    name = 'alex'
    def inner():
        nonlocal name # Find the name of the previous level
        name = 999
    inner()
    print(name)
func()
print(name)

Supplement: Global variables must all be capitalized

USER_LIST = [11,22,3]

def func():
    name = 'asdf'
    USER_LIST.append(12)
    USER_LIST.append(name)

func()
print(USER_LIST)

Posted by nova912 on Thu, 25 Apr 2019 10:54:35 -0700

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