What is? Python?

  • Dynamic interpretive language ,1982 Year by the Dutch Guido von Rossum The invention .
  • More details can be google, There is no expansion here .

Python Interpreter :

  1. CPython( Official version C Language implementation )
  2. IronPython( Can run in .NET and Mono platform )
  3. PyPy(Python Realization , Support JIT Just in time compilation )
  4. Jython( Running on the Java platform )
  • This article is only for learning Cpython be based on Python3.8+

Python Advantages and disadvantages :

  • Simple , studies of the Book of Changes , Open source , object-oriented , Scalable , Rich wheels .
  • Slow execution , Common faults of dynamic scripting languages , So computing intensive should rely on C Language and other compiler language implementation .

Python Philosophy of design

  • grace
  • clear :
  1. In a way , It's better to have only one way to do one thing
  2. If there are multiple options ,Python Developers generally reject fancy Syntax , Choose a clear grammar that doesn't differ .
  • Simple : The code is as easy to understand as pure English .
  • characteristic : All things are objects .
  • stay Python Interactive terminal input import this You can see Python zen

Python Application scenarios of

  • Web application development :Django,Flask,Tornado
  • Operating system management , Server operation and maintenance , Automation script
  • Web crawler :Scrapy
  • Scientific Computing :NumPy,SciPy,Pandas,Matplotlib
  • Desktop software ( Not very mature ):PyQt,PySide,wxPython,PyGTK
  • game
  • Server software ,APP There are also corresponding libraries , It's just that it may not be mature enough and the maintenance is not fast enough .

install Python

download Cpython Interpreter

  • visit Python Official website :https://www.python.org/
  • Click on download Button , Select the system type in the drop-down box ( windows/Mac OS/Linux etc. )
  • Select Download Python3 Version of , Suggest a new stable version

install Ptyhon

  • Double click download okay Python package
  • Check Add Python 3.8 to PATH then Install now
  • Mac and Linux Sure google Installation method , And environment variable configuration .

Test for successful installation

  • open Termal/cmd( The command line ) Input python, If the version number is displayed, the installation is successful ,

    If appear ‘python’ Not an internal or external command , Nor are they runnable programs or batch files .

    Manual configuration is required PATH, take python.exe Installation address of

    C:\\Users\Eric\AppData\Local\Programs\Python\Python38\

    Add to environment variables PATH in

Package manager pip Use

  • pip It's a modern , General purpose Python Package management tools , Provide right Python Bag

    lookup , download , install , Uninstall function , Convenient for Python Management of resource packages .
  • install : In the installation Python when , Will automatically download and install pip

pip To configure

  • In the command line , Input pip -V You can see pip Version of .
  • If appear ‘pip’ Not an internal or external command , Nor are they runnable programs or batch files , We need to be the same

    C:\\Users\Eric\AppData\Local\Programs\Python\Python38\Scripts(pip.exe Address ) Add to user PATH In the environment variables .

Use pip management Python package

  • pip install <package_name> Install the specified package , for example : pip install jango
  • pip uninstall <package_name> Delete / Uninstall the specified package
  • pip list Displays a list of installed packages
  • pip freeze And list equally , Just for package==version Format lists

    Packaging and importing environment :
  • pip freeze > requirements.txt Talking about the current environment, all modules are packaged into requirements.txt In file
  • pip install -r requirements.txt install requirements.txt The packages listed in the file

    Modify download source
  • pip install <package_name> -i as follows

    pip install flask -i https://pypi.douban.com/simple/ Download and install from Douban source flask modular

    ( Just temporarily use this Douban source , If not next time -i It's also the default source )
  • Permanent modification pip Download address :

    Create directories and configuration files C:\Users\Eric\pip\pip.ini And edit the following configuration information to save :

    [global]

    index-url=https://pypi.douban.com/simple

    [install]

    trusted-host=pypi.douban.com

    Images are commonly used in China :
  • Alibaba cloud https://mirrors.aliyun.com/pypi/simple/
  • University of science and technology of China https://pypi.mirrors.ustc.edu.cn/simple/
  • douban https://pypi.douban.com/simple/
  • Tsinghua University https://pypi.tuna.tsinghua.edu.cn/simple/
  • University of science and technology of China https://pypi.mirrors.ustc.edu.cn/simple/

    In fact, there is no need to change , A ladder is built by a wall [ funny ]

IDE

There are a lot of code editing tools , Yes vim、sublime、notepad++、VS code、Pychram etc.

The last two are recommended as integrated development environments

function

  • Run on command line py file :python hello.py

Pychram Use

  • Install the professional version directly , Respect copyright and pay ( No more Chinese characteristics or some treasure )
  • Pychram Some of the tips :
  1. Skillfully use . Number , such as a + b.print The carriage return will become print(a+b)
  2. ctrl+shift+k formatting code
  3. ctrl+ Left click the built-in function or module to quickly locate and view python Source code

Interactive programming :ipython

notes -- Help developers read code , A statement that a program will not execute

Single-line comments

# This is a single line comment pychram Shortcut key ctrl+/

Multiline comment

''' So that's one Multiline comment Three single quotation marks for multiline comments '''

Definition of variables

  • For data that is reused and often modified , Can be defined as variables to improve programming efficiency .

The syntax for defining variables

  • Variable name = A variable's value ( there = The function is to assign a value, not equal to )

    for example key = value = True = 1

    a , b = 1 , 3

    a , b = b , a # Exchange assignments

    a , *b = 1,2,3,4,5 # a=1 b = [2,3,4,5]

    python Very flexible , Very clever .

Variable name specification

  1. Cannot use keyword ( Built in keywords into print,if etc. )
  2. You can't start with a number
  3. I want to know the meaning of the name , Underline is recommended
  4. follow PEP8 standard : Variable name , Function names and file names are all lowercase , Use underscores to connect ,

    The class name follows the nomenclature of the great hump ; Constant names are all uppercase .

    The right example :student_name,user_name,user_id...

keyword

  • Some identifiers with special functions , Has been python Official use , Developers are not allowed to define the same identifier as keywords themselves .
  • See all the keywords :

    import keyword

    keyword.kwlist

    ['False', 'None', 'True', 'peg_parser', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

    None of the above can be named as a new identifier .

data type

  • int plastic
  • long Long integer [ It can also represent octal and hexadecimal ],python3 To be used as waste long
  • float floating-point
  • complex The plural
  • True Boolean type bool, really
  • False Boolean type , false
  • str character string
  • list list
  • tuple Tuples
  • dict Dictionaries
  • set aggregate

View data type

a = "123"

print(type(a)) # type() Return data type

<class 'str'> # This is a string

  • The type does not need to be declared by the developer , Define variables and ,python It's smart enough to help us define types

Output statement

  • Output / Print : Show the object results

    unfinished , Continue in the afternoon ...

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