Variable flow control

1. python History

   • Garbage collection mechanism garbage collection

   • 2004 WEB framework Django was born

   • python2：

     The source code is not uniform, there are duplicate function code

     python3:

     Source unity there is no duplication of function code

2. python is a kind of language

   • Compiled: translated only once (representative C)
     • Pros: Fast
     • Disadvantages: slow development
   • Interpreted: Progressive translation (representative python)
     • Cons: Slow execution
     • Pros: Fast Development

3. python species

   • cpython
   • Jython
   • IronPython
   • (Special) Research PyPy

4. Variables - output,

   • What is variable

     The (intermediate value storage) a temporary value stored in memory

   • Variables can do

     Variables can be reused

   • How to use variables that with frequent use -----

     a=1#声明变量
     #a ---变量名字
     #= ---赋值操作
     #1 ---值

   • Variable definition rules

     • Variable names consists of numbers, letters, underscores

     • You can not begin with a number

     • You can not use python keywords

     • You can not use Chinese and Pinyin

     • Case sensitive

     • To descriptive variable names

     • Recommended wording

       • Hump ​​body AgeOfOldboy = 98
       • Underline age_of_oldboy = 98 (the official recommended)

   • print print output

   • Senior variable small

     # age=11
     # age1=12
     # age2=age
     # age=13
     # print(age,age1,age2)
     # a=4
     # b=a+6
     # print(b)

5. Constant default all caps

   Year-round constant amount, constant declaration in the configuration file

6. Notes - explain their code, the content of the comment is not performed

   • Single-line comments (when line comments) #
   • Multi-line comments '' '' '' or "" "" "" in front of the head must write

7. The data type determines the type of base

   Int type is used to calculate it would be more

   Strings and string str only do addition, can not do with digital multiply python as long as subtraction and division caused by the string is a quoted

   Boolean value bool: True False determine the true and false

   Plus +

   Less -

   Take *

   In addition to /

   • What is the basis of type?
   • Type of foundation is doing?
   • The basis of the type that use?

8. Enter the input user interaction

   • input ( "precautionary statements")
   • Python3 content acquired all of the input string
   • int () converts the digital string into full
   • str () conversion by the variable force string type
   • type View data types

9. if --- if a keyword in python

   if True:
       #结果

   • if

   • if else a second election

     if 空格  条件 :
         缩进  结果
     else ：
        缩进 结果

   • if (if) elif (if re) selected from a plurality elif or not selected

   • if elif elif else a multiple-choice

   • if if if multiple choice

   • if the general write three nesting