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Just remember this ~

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【Python】 Silicon Valley Python Zero Basics

1-10

Configure the role of environment variables ~

• In our daily use of the command line whatever The apple system is still linux still win They all use ~

If you just write a command such as asb What happens ?

win Is the error message an internal instruction ~

Then why can some content be found ~

• It's actually because When our content can't be found in the directory of that year, we will go to -> User environment variable -> Environment variables of the system

• We just set the environment variable ~ such as js Of node vpn vpm~ You will find that you can use it directly ?

• It's actually because I found that folder ~ Found the command ~ Told the computer what to do ~

A few notes :

• path It's case insensitive ~ Path PATH All right
• mac After modification, you need to apply ,win Just reopen the window

Binary Introduction

I believe many people know the decimal system

• That is, full decimal 1; Everyone we call A hundred thousand ... I'll draw a picture
• The analogy of the two-level system is full 2 Into the 1, So name it in decimal 2 Every digit of the base is 2,4,8,16

So binary from 0 Start writing How to write ? 0,1, 10, 11, 100,101, 110, 111 , 1000, 1001, 1010 This is it. 0-10

So how do you think ?

Watch it ~ Everyone has only 0/1 1 Go up 1 If the next one is 0 It becomes 1 ; If it is 1 Just go into 0, Then the next bit continues to detect ~

( For those who have studied, you will find a very simple recursion ~

recursive : It is also called self recursion , It's calling itself , Always the same ~

Iteration is , The result of the last time will be used in the next time ~

for instance : Growth is iteration , Every year there will be changes that will affect the future , Recursion is playing games moba game , Or just say gobang , The result of the last time does not affect this time . Let's understand this first. There are many details

)

So what do you think of a 2 Into the system is 10 Decimal number ?

Let's talk about it first , commonly 2 Hexadecimal system will have a position occupation , Is similar to Contents after decimal point There will be 0 placeholder . Binary will also have... In the integer part ~

This is called Static storage space static store, There will be dynamic Of dynamic store, It will change ~ similar The shell of a tortoise ~ As the tortoise grows bigger, so does its shell , Static is equivalent to your own clothes , I'm fat eating by myself Clothes don't change , It's just tight ~

Such as it Four place , How many are the four ? 2 Of 3 Power 8 therefore The fourth place has 1 Namely 8 The number above , But it won't be 8 Of Double similar ( Thousand bit There are values on The maximum value is 9999 It can't be 10000 That's ten times )

0001 1 2 Of 0 Power =1

0010 2 The second is 2 Of 1 Power = 2

0011 3 2 The first power of + 2 Of 0 Power = 3

0100 4 2 The second power of = 4

0101 5 Two 2 Power +2 Of 0 Power = 5

0110 6

0111 7

1000 8

1001 9

1010 10

Forget it ? That position has 1 Just Use the current position -1 As 2 The index of plus that will do ~

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Mathematics is really hard to tell .... Embarrassed the math teacher ...

Why don't I write here 2^3 = 8 Because This ^ In mathematics, it represents Power But in Computer languages are bit operations ~

For example, programmers can't write 2×3=6 Can write 2*3 = 6

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data storage

This is the data 010101010 Composed of ~ But it will not be too little. Generally speaking, a number will be expressed in tens of digits ,( It doesn't unfold ~)

All arrays exist in binary form in the computer , I remember a description is diode ~ Can only off perhaps on off by 0 on by 1

Or like a small lattice ~ Can be stored 0/1

• Then each cell exists in the memory ~, We call it 1bit( position ) The bit

bit Is the smallest unit in a computer ,

8 individual bit Form a byte byte

byte Is the smallest computer Operable units ~ You can open a folder to see its size ~ Whatever you do , He can only change at least 1 byte , Will not appear to you 0.1 Bytes in this case ~

Therefore, there is the following conversion

8bit = 1 byte

1024 byte = 1 Kb(yte) kilobytes

1024 kb = 1 mb

1024mb = 1gb

1024gm = 1tb

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Now? b Are directly omitted ~

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Generally, binary will not be displayed directly , Will use 16 To display ~ Hexadecimal More than the decimal system abcedf

This one is called Binary Viewer Software for , You can open any file Displayed as binary ~

Rest assured that no one will understand .... Maybe the strongest brain can

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Insert a digression , There are a group of super intelligent people in China ~ Not all are doing research , There are... In all walks of life

They belong to a well-known group in the circle ~ within a circle ! They rated the strongest brain as --- Develop brain proficiency .

Just like the oil man we learned when we were young ~ It's hand eye proficiency , The strongest brain is Proficiency in using the brain , Always cultivate a certain area of the brain , This area will be especially powerful ~ however Other aspects will not be much more than ordinary people ~ It is still the category of ordinary people ~

The group mentioned above can search on Baidu , When we don't train, we are 5 Now After training, you may achieve 20 Those on the show may be training themselves , And can reach super high people such as 70. So these people I'm talking about may be in 50.

High IQ Association ? Forget the

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Text and character set

• The text is divided into Pure text and Rich text ~

• Plain text can only hold one type of text content , Can't save extraneous content ( typeface , Color , picture )

• Rich text can save something other than text , Software example word file pdf

• At development time , The program is written in plain text ~( It would be awesome if you could develop with pictures ... Put a picture on it and directly generate plain text ..., Then add audio development ,hhh)

• Plain text is converted to at the bottom of the computer 2 Hexadecimal code ~

  • Since it can be converted, it needs an agreement ? Rules ?

    • Character conversion binary is called --- code
    • Binary conversion characters are called --- decode
  • The rules followed by encoding and decoding are called character sets ~

• Common character sets :

  • ASCII

    • American
    • Is the total 128 Seven But it must occupy one byte The highest bit is 0
    • Case write + A pile of symbols altogether 128 individual Quite enough ~

    Followed by Roman numerals 2, And then there was ASCII Expand Expanded 1 position 2 Of 8 Power = 256 But many languages can't put everything in 256 This code is not used in bits ~

  • ISO-8859-1

    • European Code
    • Is the total 256 8 position

  • GB2312

  • GBK

    • The above two are both in Chinese , There is nothing special , My name is a rare word ~ At first there was no , It's all added ~

  • Unicode

    • unicode ~ Contains all the languages and symbols
    • You can baidu Unicode, Look at your name ~
    • Unicode There are many implementations , Include UTF-8 UTF-16 UTF-32

      • UTF-8 It's getting longer May be 1-5 Bytes to represent a character
      • UTF-16 yes 2-4
      • UTF-32 Is constant 4 Bytes
      • It's usually UTF-8

The statement

The above understood words Think about why the garbled code phenomenon ?

• It is not a rule to decode and encode ~
• So if there is garbled code, check whether the character set is the same ~

Computer language

Computer languages are divided into machine language , Semiotic language ( assembly language ), High-level language . Computer language is talking to computers ~

• machine language :

  • The binary
  • Efficient execution but not easy to write

• assembly language :

  • Know that the machine is not easy to write , Then it's just a little easier to write , Replace part of machine language with symbols ~ Then the symbols are converted into machine language
  • This process is called assembly assembling, The process of turning back is called disassembly disassembling
  • Better write some , The execution efficiency is not so slow ~
  • Assembly language can only be applied to some hardware , Poor compatibility ~

• High-level language :

  • Just like that. python This kind of language is better understood and learned . But it will be less efficient ~ So the chain of disdain appears in high-level languages ~
  • The closer to the assembly, the higher the learning cost, such as c derivatives ~hhh doge. At the top of the chain of disdain . Of course, the big guys who play these games usually don't bully the rest of us
  • Grammar is similar to English , But the connection with hardware is not so close ~
  • C C++ C# Java python js

Introduce what is interpreted language and compiled language

• High level languages also need to be converted into machine code and then executed

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Pay attention to this , I remember mentioning in the university that , High level languages need to be converted into assembly and then into machine code ~ In fact, there is no need to convert to assembly language at all , There is no need to compile as a bridge ~ High level languages are translated into opcode The efficiency of machine code is also very fast and accurate

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According to the timing of the conversion ~ Language is divided into interpretive language and compiled language

• Compiler language

  • C Language ,
  • Compile the code into before the code is executed opcode And then let the computer handle it
  • Execution speed special fast
  • But poor compatibility , For example win Compiled in mac The system cannot be used , stay linux Compiled in win I can't use ~

• Explanatory language

  • Python Javascript Java
  • The code parses as it executes
  • The speed will be relatively slow , But cross platform will be good

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  To put it bluntly, it is a precompiled , An implementation is bound to be slow during compilation ~ Cross platform depends on the interpreter ~ So where is the difference between speed ? The efficiency of the interpreter will determine the execution rate to some extent ~

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java It's interpreted language ,Java It's compiled first class file , Re pass JVM Explain to perform , It's an interpretative language

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use python Some gadgets you must know

• python Inventor Guido Guido Gui Uncle GUI ~ It is called this name in China

  • 19 Retired in senseless 20 Joined Microsoft in 1996

• There is a saying. ''Life is short I use Python' Life is too short for me python

• python The design of the schedule

Write a few Python Use of :

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Count as flag Well , I will play it all for the last time ~ After all, Kudo doesn't have to do it himself ~2333

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• Web application
• Reptiles
• Scientific Computing
• Automatic operation and maintenance
• big data
• Cloud computing
• Ai
• game ( This is not done )

python Environment building

To put it bluntly, setting up an environment is to install an interpreter ~

python There are many versions of the interpreter for

• CPython( official )

  • use C Written language
• Pypy

  • use python Written python Interpreter
• IronPython

  • use .net Written
• Jython

  • Java Written

python edition

python There are two big versions

2.x and 3.x

There is a difference here ,

• This version does not say 3.x It's better than 2.x The best ~ The two of them are parallel All in use

• 3.x And 2.x Are incompatible with each other ~

I must learn something new ~ So the following syntax is 3.x The grammar of ~

OK install Python

I'm using mac, So use homebrew download ~

• homebrew yes mac Our package management tools are very powerful ~

Homewbrew download

The terminal can input this sentence , I've been looking for a long time ! Pay attention to the execution process , Very meticulous ~

/bin/zsh -c "$(curl -fsSL https://gitee.com/cunkai/HomebrewCN/raw/master/Homebrew.sh)"

After installation, you need to configure the domestic image ~ Just choose ~

Then install python Version management tools , because python There are many versions ~ Switching is troublesome. With this switch, just enter a code ~

brew install pyenv
pynev install 3.10.0

that will do ~

Input python Later >> Proof of successful installation ~

It's called entering python The interaction mode of

win That's true

• mac That's true , You can see that I have entered python

• The version is mac Self contained version 2.7

• How can I cut it into the ones I downloaded ? Use the version control tool

• Enter this command to exit interactive mode

pyenv global 3.10.0

that will do

We certainly don't use terminal development ~ Write small demo It won't be here , Find a web page to edit online python All good. ~

ok It's here today ~