1, Foundation

1. Language related issues

• Q: what are the characteristics and advantages of python?

Features: python is an interpretive language. The code is interpreted and executed through the interpreter. The code that is executed is interpreted. There is no need to precompile to generate executable files.

Disadvantages of interpretive language: it relies too much on the interpreter environment. The interpreter is a virtual environment. Before running the code, you have to apply for memory, open up space, start the interpreter and consume more memory.

python disadvantages: low execution efficiency

Advantages of Python: high code writing efficiency, fast development speed and good cross platform (one-time development, running everywhere, as long as there is a python parser on Window, Linux and Mac, you can run Python code). It is relatively easy to learn and there are many open source projects.

• Q: why do you use python for development and how did you get started with python development?

You can list the reasons: you learned python in college, and you learned python in your internship. You find python very interesting: say the advantages of the previous question...

• Q: what language have you used when you came out of python?

JavaScript (must know, web page scripting language, and JS language is used in vue)

• Q: what is a compiled language

Compiled languages need to be compiled first to generate a binary file, such as C, and generate an exe executable file; Then it's executing.

Advantages: high execution efficiency.

Disadvantages: debugging bugs is troublesome, and the process of writing code is slow to produce results (the effect cannot be seen immediately after writing code, so it needs to be compiled and executed first)

2. python PEP8 specification

PEP8 specification is the guiding specification for python code writing. It is not a syntax error, but a writing specification. (if it is not observed, the code will not report an error)

Indent each line with 4 spaces

The maximum number of characters for all lines is 79

It is not recommended to import multiple modules in one row (one module in one row)

It is easy to make mistakes without using single character as variable name (1 and 0 are like I and O)

Class names should be capitalized; Function names should be lowercase. If you want to improve readability, you can separate them with underscores.

3. What are the common codes

ASCII 1 byte English language (0-9 a-z A-Z characters)

GBK 2-byte Chinese code supports traditional characters

UTF-8 variable length code (1-3 bytes) universal code supports various languages

1. In order to process English characters, ASCII code is generated.
2. In order to process Chinese characters, GB2312 is generated.
3. In order to process national characters, Unicode is generated.
4. In order to improve the storage and transmission performance of Unicode, UTF-8 is produced, which is an implementation form of Unicode

2, python Foundation

1. The difference between p2 and p3

1, python2 use print Print   python3 use print()Method printing
2,python2 The result of division is an integer    python3 The result of division is floating-point data, and the double slash is required for integer division//
3,python2 Default is ASCII Code to use unicode Need special definition unicode String example u'hello'
python3 Default is unicode(utf-8)character string
4,p2 The advanced function returns list  p3 Returned by advanced function iteration iterator 

2. is and = = difference

==True as long as the values are the same

is requires not only the same value, but also the same address to be True

For example, if x = 1 and y = 1, x is y is True. This is because there is a constant pool in python, 1 belongs to the constant pool, and X and Y refer to the same constant, so their addresses are the same.

For example, x=[1,2,3] y=[1,2,3] x==y is True, but x is y is False because X and y are different memory spaces and address pages are different

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3.range and xrange

I haven't used xrange. I've used range. Range represents a range, and the range function returns an iteratable object), not a list type. The range function in Python 2 returns a list.

range(1,5) does not include 5. Generally, the parameters of this interval in python are greater than or equal to the latest value and less than the maximum value

According to my investigation, when Python 3 returns the list, it returns the iteratable object instead of directly returning the list.

4. Ternary expression

true expression if judgment expression else false expression

y= 20 if x==3 else 10

5. Interchange variables

x,y=3,4

x,y=y,x

Can be achieved x And y The exchange of values by x=3  y=4  Instead x=4  y=3

Sequence unpacking sequence packet

6. Deep copy and shallow copy

• Shallow copy: only the first layer is copied, and no deep layer is copied. Modifying the first layer does not affect each other. Modifying the second layer affects each other.

• Deep copy: a recursive copy will generate a set of exactly the same content in memory, and the modification will not affect each other

Slicing is a shallow copy.

x = ["1", "2", ['a', 'b', 'c'], "3", "4", "5"]

y = x[:3]
print(id(x), id(y))
y[2].append('k')
print(x, y)

7. Introspection of python

When the program is running, it can get the information of the object, 3 properties and 2 types

Introspective attribute	introduce	use
dir	Get all properties in the object (properties and methods; properties and methods inherited from the parent class)
type	View the type of object
hasattr	Determine whether there is an attribute in the object
getattr	Get the property value of the object according to the property name
isinstance	Determine whether the object is a type

Case:

class Student:
    country = "China"

    def __init__(self, name, age=None):
        self.name = name
        self.age = age

    def say(self):
        print("I am{}")
        return "OK"


def add():
    print("add")


if __name__ == '__main__':
    s = Student("Zhang San")
    print(dir(s))  #
    print(type(s))
    print(hasattr(s, "gender"))
    print(getattr(s, "name"))
    print(getattr(s, "say")())
    print(isinstance(s, list))
    print(isinstance(s, Student))

8. CSV file, what is it

Comma separated values (CSV, sometimes referred to as character separated values, because the separating character can also be not a comma), and its file stores tabular data (numbers and text) in plain text

Simply put: store table type data in plain text

#test.csv

full name,Age,occupation,Native place,wages
 Cao Cao,33,student,Henan,8000
 Liu Bei,53,student,Sichuan,5000
 Sun Quan,23,student,Jiangsu,6000

Our python provides a csv module, which can realize the operation of csv

import csv


def writeTO():
    with open("D:\\test.csv", 'w', newline='') as f:
        rowh = ["full name", "Age", "occupation", "Native place", "wages"]
        row1 = ['Cao Cao', '33', 'student', 'Henan', '8000']
        row2 = ['Liu Bei', '53', 'student', 'Sichuan', '5000']
        row3 = ['Sun Quan', '23', 'student', 'Jiangsu', '6000']
        write = csv.writer(f)
        write.writerow(rowh)
        write.writerow(row1)
        write.writerow(row2)
        write.writerow(row3)
        print("Write complete!")


def readCVS():
    with open("D:\\test.csv", 'r') as f:
        r = csv.reader(f)
        row_header = next(r)
        print(row_header)
        for row in r:
            print(row)
            
# Print effect

['full name', 'Age', 'occupation', 'Native place', 'wages']
['Cao Cao', '33', 'student', 'Henan', '8000']
['Liu Bei', '53', 'student', 'Sichuan', '5000']
['Sun Quan', '23', 'student', 'Jiangsu', '6000']

9. What compression types are available

tar: knowledge packs multiple files together, not a compressed format.

zip: the most common compression format, which is relatively fast.

rar: the file compression ratio is higher than zip, but the compression speed is slow and the random access speed is slow.

10. Persistence

Talk about the persistence of transient data (data in memory) into persistent data (stored in files and databases)

JSON module is to persist the JSON format, using JSON Load (FP)

11. Parameters

12. Recursion

– handwritten code

Recursively write Fibonacci sequence, factorial, variable file directory

Fibonacci sequence

1  1  2  3  5  8  13  21
f(n-2)+f(n-1)=f(n)
"""


def f(n):
    if n == 1 or n == 2:
        return 1
    return f(n - 1) + f(n - 2)


for i in range(1, 10):
     print(f(i), end=" ")

'''
Recursive traversal of file directory
'''
path = "E:\\Cumulus education materials\\2021 Annual data"

import os  # The interface between python and sys is provided by the underlying parser

def fileRead(path, level=1):
    for file in os.listdir(path):  # listdir(path) gets all the files (files, directories) in this directory
        # Print all files and subdirectories of a directory
        print("%d%s%s" % (level, level * '-', file))
        # If this is a directory
        if os.path.isdir(os.path.join(path, file)):
            # Then recursively call to traverse the subdirectory
            fileRead(os.path.join(path, file), level + 1)


fileRead(path)

14. Regular

• Matching pattern

1,Greedy model
 By default, regular expression search tends to the maximum matching. As many matching characters as possible is the greedy pattern


2,Non greedy model
 Regular expressions match as few characters as possible when searching. Use question marks? After the number of matching characters is reached, the non greedy mode is realized

case:
*? *The number is matched by the least matching mechanism, that is, 0 times     (* Indicates that the subexpression appears 0 or more times, which can be 0 times)
+? +The least matching mechanism of the number, that is, once(+ Indicates that the subexpression occurs one or more times, at least once)

• Match times metacharacter

{m,n} Specify the number of matches  m reach n second
{m} Matching times greater than or equal to m second
?  The number of matches is 0 or 1
+  The number of matches is 1 or more
*  The number of matches is 0 or more

• Common regularization methods

re.match 

Match a string that conforms to the rule from the beginning, starting from the starting position
 An object is returned when matching is successful, but not successfully None

re.search

The function looks for a pattern match within the string, starting anywhere in the string
 Returns if the string does not match None

15. random module

python in random The module is used to produce random numbers

random.random 
Used to produce a random floating-point number from 0 to 1:

random.randomint(a,b)
Used to produce one[a,b] Integer in range

random.choice(seq)
Used to randomly select an element from a sequence

random.shuffle(list)
Used to disrupt elements in a list  # This is to modify the list itself. If you disturb its order, it must be modifiable. Therefore, you can't disturb the order with strings and tuples. You can only modify the list

16. json module

import json

dic = {"name": "Tom", "age": 22, "gender": "male"}

s = json.dumps(dic, ensure_ascii=False)
print(s,type(s))
r=json.loads(s)
print(r,type(r))

17. Partial function

Partial function can fix the parameters of the function, which is convenient to use and call

"""Partial function"""
import functools


def add(x, y, z):
    print(x, y, z)
    return x + y + z


add1 = functools.partial(add, 10)

print(add1(20, 30))
print(add1(15, 60))

add2 = functools.partial(add1, 20)

print(add2(100))

2, Object oriented

1. Object oriented understanding

Encapsulation:

Succession:

Polymorphism:

2. Multiple inheritance

MRO  Continue search order

Used to determine the order in the case of multiple inheritance

python3 Breadth first algorithm

3. And super self

super is a method that can get the parent class in the subclass. super can also be used to actively solve multiple inheritance problems

Self is used to point to the current instance. In the class, the attribute pointed to by the self pointer is an instance attribute, which can only be accessed by the instance

When an instance calls a method, the first parameter self of the instance method will be automatically passed into the current instance,

4. Main magic methods

__new__

__init__

__call__

__del__

5. Method, class, method attribute

6. Metaclass

Singleton mode

7. Algorithm

7.1 binary search

Binary search, also known as half search algorithm,

Simple binary search takes little time, and its spatial complexity is O(1) and time complexity is O(logN)

Note: dichotomy search is a quick search for ordered data sets

# Dichotomy search -- circular search

def find_while(list, val):
    left = 0
    right = len(list) - 1
    while True:
        if left > right:
            return -1
        middle = (left + right) // 2
        print("left:{} right:{} middle:{}".format(left, right, middle))

        if list[middle] == val:
            return middle
        elif list[middle] < val:
            left = middle + 1
        else:
            right = middle - 1



# Dichotomy search -- recursive search
def find_digui(list, val, left, right):
    if left > right:
        return -1
    middle = (left + right) // 2
    print("left:{} right:{} middle:{}".format(left, right, middle))

    if list[middle] == val:
        return middle
    elif list[middle] < val:
        left = middle + 1
    else:
        right = middle - 1

    return find_digui(list, val, left, right)

8. Common mode

8.1. Handwriting single example mode

class Student:
    __instance = None  # Judge__ Whether the instance property is None

    def __new__(cls, *args, **kwargs):
        if cls.__instance is None:
            cls.__instance = super(Student, cls).__new__(cls, *args, **kwargs)
            return cls.__instance
        else:
            return cls.__instance


if __name__ == '__main__':

    stu = Student()

    stu1 = Student()
    stu2 = Student()
    print(id(stu), id(stu1), id(stu2))

9. Monkey patch

The main function of monkey patch is to add and change the functions without changing the source code. It is particularly useful when some third parties are not satisfied in the programming process

Is a programming skill.

class Student:
    age = 30

 
    def run(self):
        print("Run fast, run fast")


def new_run(*args):
    print("Who am I?,who are you!")


def hello(*args):
    print("hello everyone!")


if __name__ == '__main__':
    stu = Student()

    stu.run = new_run

    stu.hello = hello

    stu.run()

    stu.hello()

10. Iterators and iteratable objects

have __iter__    __next__ The object of the magic method becomes an iterator

Iteratable objects are also implemented__iter__Method, not necessarily implemented__next__  
Iteratable objects are supported for Cyclic iteration
 Lists, tuples, strings, and dictionaries are all iteratable objects

Functions that can produce iterators (iterator generator)

count(start,step) produces infinite return iterators

import itertools
import time

iter1 = itertools.count(1, 2)
for i in iter1:
    print(i)
    time.sleep(2)

1  3  5  7  9

Obj iterator

iter2 = itertools.repeat([1, 2, 3])

for i in iter2:
    print(i)
    time.sleep(2)

[1, 2, 3] [1, 2, 3]  [1, 2, 3]  [1, 2, 3]  [1, 2, 3]

3, Threads and processes

1. Thread, process

2. Synergetic process

3. yield implementation process

4. Lock and semaphore

5. GIL lock

4, Network foundation

1. C/S and B/S architecture

2. OSI layer 7 and TCP layer 4

3. TCP heartbeat packet

4. Multiplex IO

5. Blocking and non blocking

6,select,poll,epoll

5, Advanced programming

1. Reflection

2. Monkey patch

3. Iterator

4. Generator

5. Design mode

5, Algorithm

1. Binary search

2. Select sort

3. Bubble sorting

4. Quick sort

itertools
import time

iter1 = itertools.count(1, 2)
for i in iter1:
print(i)
time.sleep(2)

1 3 5 7 9

repeat(obj)  Production repeat iterator

iter2 = itertools.repeat([1, 2, 3])

for i in iter2:
print(i)
time.sleep(2)

[1, 2, 3] [1, 2, 3] [1, 2, 3] [1, 2, 3] [1, 2, 3]

## 3, Threads and processes

### 1. Thread, process



### 2. Synergetic process



### 3. yield implementation process



### 4. Lock and semaphore



### 5. GIL lock



## 4, Network foundation

### 1. C/S and B/S architecture





### 2. OSI layer 7 and TCP layer 4





### 3. TCP heartbeat packet



### 4. Multiplex IO



### 5. Blocking and non blocking



### 6,select,poll,epoll





## 5, Advanced programming

### 1. Reflection





### 2. Monkey patch





### 3. Iterator



### 4. Generator



### 5. Design mode



## 5, Algorithm

### 1. Binary search



### 2. Select sort



### 3. Bubble sorting



### 4. Quick sort