Day2- syntax basis and variables

Summary of learning

The output function is to output the data in the program to the console
Input function ： The program obtains data from the console

1.input function ( adopt input The result of the input data is a string , Cannot be applied to operations , To convert )

Variable = input( Enter the prompt message ) - Prompt the user to enter content , And save the input to the variable

age = input(' Please enter your age ：')
print(age)

# Prompt the user for name, age and phone number

name = input(' Please enter your name ：')
number = input(' Please enter your phone number :')
print(name, number)
print(' full name ：',name, ' Telephone ：', number)

2. Output function

print Is to display the data in the program on the console （ Print ） come out , All the contents displayed on the console must be print Printed content

1） Basic usage

a. One print Print a data

b. One print Print multiple data ：print( data 1, data 2, data 3,…)

print(10, 20, 3,)
print(type(10.3), 10 + 2, type(' Hello '))
number = 11233
print(number)

2) Advanced usage

By default, a print The printed content occupies one line

a. customized end：print（ data 1, data 2, end=’’）

Printing principle ： Program designation print During operation , Will print the data first , And then print it end Value （end The default is line feed ）

print(12, 15, end=' ')
print(11)
print(12)

If you want a blank line, enter an empty print（）

print(11,end=';')
print(1)
print()
print(3)

b. customized sep

customized sep It is used to control when printing data at the same time , How data is separated from data , Default is space

print(1, 2, 3, sep=',')
print(1, 2, 3, sep=';')
print(1, 2, 3, sep='\n')    # \n  It's line changing 

print(1, 3, 2, sep=',', end=';')
print(1, 3, 2, end=',', sep=';')

3. notes

1) Single-line comments

ctr +/ Automatic generation

2） Multiline comment

Put the content between double quotation marks or single quotation marks in three English States

3） The function of annotation

a. Annotate the code with , Improve the readability of the code

b. Cancel code function

4. Lines and indents

1） That's ok

python One line of code , You can leave a semicolon at the end of a line

print('hello')
print(' Hello ')

If you have to display multiple statements on one line , Semicolons must be used between statements

print('hello');print(' Hello ')

2） Indent - The space before a statement is called indentation

A statement cannot be preceded by a space

5. Identifiers and keywords

1) identifier - Naming requirements

python Identifier requirements ： By letter 、 Numbers or underscores , And numbers don't start ( There can be no symbols other than these three )

a = 100
a1 = 100
a1_ = 100

2） keyword - python Some identifiers with special functions or special meanings in

Print all keywords

from keyword import kwlist
print(kwlist)

6. Common data and data types
1) Digital data ： Data used to represent the size of a numeric value , For example, age 、 height 、 distance , amount of money
The method of representing digital data in a program ： The same way that numbers are represented in Mathematics , Support scientific counting
The type corresponding to the number ： Digital data is divided into integer types （int） And floating point （float） Two kinds of
2） Text data ： It is used to represent the data corresponding to text information , for example ： full name , Address , School name , Phone number , Zip code , Id card number
Representation ： Text data must be enclosed in double or single quotation marks
type ： character string （str, Abbreviations of words ）
3） Boolean data : Only True and False Two values ,True It means true , To affirm ,False It means false , Denying
（True and false Is the key word ）
Representation ： direct writing True perhaps False, Don't add any characters
type ： Boolean （ English translation ,bool）
4） Null value :None( It means nothing )
keyword ：None
type ：None Type

7. operation

1） Get data type ：type( data ) - Gets the type of the specified data

type(3.2)
print(type(3.2))
print(type(True))
print(type(' Hello '))

character string （ Text data ）

2） Type conversion ： Type name in parentheses - Converts the specified data to the specified type

 take 10.9 Convert to integer 

int(10.9)
print(int(10.9))

Homework

choice question

1. B
2. C
3. B
4. C
5. D

Completion

1. #; “”“ ”“”
2. 10;20
3. .py
4. integer
5. Single quotation marks ; Double quotes
6. two ;Ture、False
7. type

Programming questions

x = str(input(' Please enter a user name ：'))
y = int(input(' Please input a password ：'))
print(' user name ：', 'x', ' password ：', y)

x, y, z = 1, 2, 3
print(x, y, z, sep='=')

Short answer

1. The variable name is named by the programmer ; Is an identifier. , It can't be a keyword ; When you choose a name, you should see the name and know the meaning , Do not use system function names 、 Class name and module name , The letters are all lowercase , Multiple words are separated by underscores .

2. 1） Easy to learn

2） High development efficiency

3） Explanatory language , Platform portability

4） It supports both mainstream programming paradigms

5） The degree of standardization , High readability

3. 1） Data analysis

   2） Artificial intelligence

   3） Quantum trading

   4） Network data collection

   5） automated testing

   6） machine learning