Python Basics 3-Basic use and naming of variables

4. Basic use of Variables 4.1 variable definition

• In Python, each variable must be assigned before it is used, and the variable will be created after the variable is assigned .
• The equals sign (=) is used to assign a value to a variable
  • = Left is variable name
  • = right is the value stored in the variable

Variable name = value

After the variable is defined, the following can be used directly

4.2 Types of variables

• Creating a variable in memory will include:

Name, saved data, type of stored data, address (label)

• Defining a variable in Python does not require a specified type (required in many other high-level languages)
• Data types can be divided into digital and non-digital
• Digital type
  • Integral type (int)
  • Float type (float)
  • Boolean type (BOOL)
    • True true not 0 number--nonzero is true
    • False false 0
  • Complex Type (complex)
    • Mainly used for scientific calculation, such as: Plane field problem, fluctuation problem, inductance capacitance and so on.
• Non-digital type
  • String
  • List
  • Meta-group
  • Dictionary

Tip: In Python 2.x, integers are divided according to the length of the saved values:

• • Int (integer)
  • Long (length integer)
  • You can see the type of a variable using the type function

In [1]: type (name)

　　

4.3.1 calculation between different types of variables

1) The number of variables can be calculated directly between

• In Python, two numeric variables are available for direct arithmetic operations.
• If the variable is of type bool, at the time of calculation
  • True the corresponding number is 1
  • False the corresponding number is 0

2) use + stitch string between string variables

• In Python, a new string can be generated using + stitching between strings

In [1]: first_name = "three" in [2]: last_name = "Zhang" in [3]: First_Name + last_nameout[3]: ' Three sheets '

　　

3) string variables can be used with integers * to repeatedly stitch the same string

In [1]: "-" * 50out[1]: '--------------------------------------------------'

　　

4) No other calculations between a numeric variable and a string

In [1]: first_name = "Zhang" in [2]: x = 10In [3]: x + first_name---------------------------------------------------------- -----------------typeerror:unsupported operand type (s) for +: ' int ' and ' str ' types error: ' + ' unsupported operation type: ' int ' and ' str '

　　

Input of the 4.3.2 variable

• The so-called input , is to use code to get the user input information through the keyboard
• In Python, if you want to get the user's input on the keyboard , you need to use the input function

Function	Description
Print (x)	Output x to the console
Type (x)	View the variable type of x

• In Python, you can use the input function to wait for the user's input from the keyboard
• any content entered by the user Python is considered a string

String variable = input ("hint message:")

　　

type conversion function

Function	Description
int (x)	Convert x to an integer
Float (x)	Convert x to a floating-point number

defines a floating-point variable to be converted using the FLOAT function while receiving user input

Price = Float (Input ("Please enter prices:"))

　　

Formatted output of 2.5 variables

Apple price 9.00 yuan/catty, purchased 5.00 pounds, need to pay 45.00 yuan

• Use the print function to output formatted content
• % is called the format operator , which handles string formatting
  • contains a string of%, is Called format string
  •  % with different character , different types of data need to use Different formatting characters

format character
%s	string
< P class= "compact" >%d	signed decimal integer,%06d indicates the number of digits of the output, 0 complement
%f	floating-point number,%.2f indicates only two digits after the decimal point /p>
%%	output%

Print ("formatted string"% variable 1) print ("formatted string"% (variable 1, variable 2 ...)) Print ("My name is%s, please take care!") "% name" print ("My school number is%06d"% student_no) print ("Apple unit price%.02f yuan/kg, purchase%.02f Catty, need to pay%.02f yuan"% (prices, weight, money)) print ("Data Ratio is%.02f%% "% (scale * 100))

　　

Practice-- Personal Card

Demand

• Prompt user input in the console: name , company , position , phone , email
• Output in the following format:

Company name Name (position) Tel: e-mail: Email **************************************** **********

　　

Code:

"" In the console prompts the user to enter: name, company, position, phone, email "" "Name = Input (" Enter name: ") company = input (" Please enter Company: ") title = input (" Please enter position: ") phone = input ("Please enter the phone:") email = input ("Please enter the mailbox:") Print ("*" *) print ("*" * "*") "Print" ("%s"% (name, title)) Print ("Tel: %s "% phone" print ("Mailbox:%s"% email) print ("*" * 50)

　　

5. Name of the variable 5.1 identifier

Identifiers are programmer-defined variable names , function names

• Identifiers can consist of letters , underscores , and numbers
• Cannot start with a number
• cannot be duplicate with keyword
• The keyword is the identifier that has been used inside Python
• keywords have special features and meanings
• Developers are not allowed to define identifiers with the same name as keywords

5.2 Key Words

Use the following command to view the keywords in Python

In [1]: Import Keywordin [2]: print (keyword.kwlist)

　　

• Import keyword can be imported into a " Toolkit"
• Different toolkits in Python, with different tools available

5.3 Naming conventions for variables

naming rules can be considered as a convention , and there is no absolute and mandatory purpose to increase the identification and readability of code

Note identifiers in Python are case-sensitive

1. When defining variables, the left and right of the = should keep a space
2. In Python, you can name it in the following ways
   1. Use lowercase letters for each word
   2. Use the underline connection between words and words

For example: first_name, last_name, Qq_number, Qq_password

Hump Naming Method

• The small hump-type naming method

The first word starts with a lowercase letter, and the first letter of the subsequent word is capitalized. For example: FirstName, LastName

• The large hump-type naming method

The first letter of each word is capitalized. For example: FirstName, LastName, CamelCase

Python base 3-basic use and naming of variables