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This article focuses on "the basic use of python variables", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "the basic usage of python variables".

Basic use of variables

Programs are used to process data, and variables are used to store data.

target

Variable definition

Type of variable

Naming of variables

01. Variable definition

In Python, each variable must be assigned before it is used, and the variable will not be created until the variable is assigned

The equal sign (=) is used to assign a value to a variable * = on the left is a variable name * = on the right is the value stored in the variable

Variable name = value

After the variable is defined, it can be used directly later.

1) variable exercise 1-the variable iPython# defines qq_number is used to save the qq number In [1]: qq_number = "1234567" # output content saved in qq_number In [2]: qq_numberOut [2]: '1234567 definition # variable used to store qq password In [3]: qq_password = "123" # output content stored in qq_password In [4]: qq_passwordOut [4]:' 123'

In an interactive way, if you want to view the contents of a variable, you can enter the variable name directly without using the print function.

2) variable exercise 2-- PyCharm# defines qq number variable qq_number = "1234567" # defines qq password variable qq_password = "123" # in the program, if you want to output the contents of the variable, you need to use the print function print (qq_number) print (qq_password)

Use the interpreter to execute, and if you want to output the contents of a variable, you must use the print function

3) variable exercise 3-- buy apples in the supermarket

You can use the calculation results of other variables to define variables

After the variable is defined, it can be used directly later.

Demand

The price of apples is 8.5 yuan per jin.

Bought 7.5 jin of apples.

Calculate the amount of payment

# define Apple price variable price = 8.00 define purchase weight weight = 7.0calculated amount money = price * weightprint (money) thinking question

If you just buy an apple, you will return 5 yuan.

Please recalculate the purchase amount

# define the Apple price variable price = 8.00 define the purchase weight weight = 7.0calculated amount money = price * weight# if you buy an apple, you will return 5 yuan money = money-5print (money)

Ask a question

How many variables are defined in the above code? * three: price/weight/money

Is money = money-5 defining new variables or using variables? * directly use the previously defined variable * the variable name is defined only when it appears for the first time * the variable name appears again, not to define the variable, but to use the previously defined variable directly.

In program development, can you modify the values saved in the previously defined variables? * can * the value stored in the variable can be changed

02. Type of variable

Create a variable in memory that includes: 1. The name of the variable 2. The data stored in the variable 3. Variable stores the type of data 4. The address of the variable (marked)

2.1 Walkthrough of variable types-personal information

Demand

Define variables to save Xiao Ming's personal information

Name: Xiao Ming

Age: 18

Gender: male

Height: 1.75m

Weight: 75.0 kg

Use single-step debugging to confirm the type of data saved in the variable

Ask a question

How many data types are there in the walkthrough? * 4 kinds of * str-string * bool-Boolean (true or false) * int-integer * float-floating point number (decimal)

Do you need to specify a type when defining variables in Python? * not necessary * Python can automatically deduce the type of data stored in the variable according to the value to the right of the = equal sign

2.2 types of variables

It is not necessary to specify a type to define a variable in Python (required in many other high-level languages)

Data types can be divided into digital and non-digital types.

Digital * integer (int) * floating point (float) * Boolean (bool) * true True non-zero-true * false False 0 * complex (complex) * is mainly used in scientific calculations, such as plane field problems, wave problems, inductance and capacitance problems, etc.

Non-numeric * string * list * tuple * dictionary

Tip: in Python 2.x, integers are also divided into:

* int (integer) * long (long integer)

Use the type function to view the type of a variable

In [1]: type (name) 2.3 calculation between different types of variables 1) numeric variables can be calculated directly

In Python, two numeric variables can be calculated directly.

If the variable is of type bool, the number corresponding to * True is 1 * False and the corresponding number is 0.

Rehearsal steps

Define the integer I = 10

Define floating point number f = 10.5

Define Boolean b = True

In iPython, the above three variables are used to perform arithmetic operations on each other.

2) use + concatenation strings between string variables

In Python, you can use + splicing between strings to generate new strings

In [1]: first_name = "three" In [2]: last_name = "Zhang" In [3]: first_name + last_nameOut [3]: 'three' 3) string variables can be used as integers * to repeatedly concatenate the same string In [1]: "-" * 50Out [1]:'- -'4) No other calculations can be performed between numeric variables and strings In [1]: first_name = "zhang" In [2]: X = 10In [3]: X + first_name-- -- TypeError: unsupported operand type (s) for +: 'int' and' str' type error: `+` unsupported operation types: input of `int` and `str`2.4 variables

The so-called input is to use code to obtain the information entered by the user through the keyboard.

For example, go to the bank to withdraw money and enter the password on ATM

In Python, if you want to get the user's input information on the keyboard, you need to use the input function

1) about functions

A pre-prepared feature (code written by others or yourself) that can be used directly without paying attention to internal details

Functions that have been learned so far

Function description print (x) outputs x to the console type (x) View the variable type of x 2) input function realizes keyboard input

In Python, you can use the input function to wait for user input from the keyboard

Anything entered by the user is considered to be a string by Python

The syntax is as follows:

String variable = input ("hint:") 3) Type conversion function description int (x) converts x to an integer float (x) converts x to a floating point number 4) variable input exercise-supermarket Buy Apple enhanced version

Demand

The cashier enters the price of the apple, unit: yuan / jin

The cashier enters the weight of the apple purchased by the user, in jin

Calculate and output the payment amount

Exercise method 1. Enter Apple unit price price_str = input ("Please enter Apple price:") # 2. Require Apple weight weight_str = input ("Please enter Apple weight:") # 3. Calculate amount # 1 > convert Apple unit price to decimal price = float (price_str) # 2 > convert Apple weight to decimal weight = float (weight_str) # 3 > calculate payment amount money = price * weightprint (money)

Ask a question

In the drill, how many variables are defined for the price? * two * price_str records the price string entered by the user * price records the converted price values

Think about it-is it convenient for users to enter many numbers through the console and define two variables for each number in development?

Exercise method 2-buy an improved version of Apple

When a floating-point variable is defined to receive user input, the float function is used for conversion

Price = float (input ("Please enter price:")

Benefits of the improvement:

Save space, you only need to allocate space for one variable

It is convenient to name, and there is no need to name intermediate variables.

Improved "shortcomings":

Beginners need to know that the two functions can be used in nesting, which is slightly more difficult.

Prompt

If you do not enter a number, there will be errors in the execution of the program. The advanced topic about data conversion will be discussed later!

2.5 formatted output of variables

The unit price of Apple is 9.00 yuan per jin. If you buy 5.00 jin, you need to pay 45.00 yuan.

In Python, you can use the print function to output information to the console.

If you want to output text information as well as data, you need to use the formatting operator

% is called the format operator and is specially used to deal with the format * containing% in the string, which is called the format string *% and is used in conjunction with different characters. Different types of data need to use different format characters.

Format character meaning% s string% d signed decimal integer, d represents output integer display digits, deficiency uses 0 to complete% f floating point,% .2f indicates that only two%% output% is displayed after the decimal point.

The syntax format is as follows:

Print (format string% variable 1) print (format string% (variable 1, variable 2...)) Formatting output walkthrough-basic exercise

Demand

Define string variable name, output my name is Xiaoming, please take care of me!

Define integer variable student_no, output my student number is 000001

Define decimal price, weight, money, export apple unit price 9.00 yuan / jin, buy 5.00 jin, need to pay 45.00 yuan

Define a decimal scale, the output data ratio is 10.00%

Print ("my name is% s, please take care of me!" % name) print ("my student number is d"% student_no) print ("Apple unit price% .02f / jin, purchase% .02f jin, need to pay% .02f yuan"% (price, weight, money)) print ("data ratio is% .02f%"% (scale * 100)) after-class exercises-personal business cards

Demand

Prompt the user for input in the console: name, company, position, phone number, mailbox

Output in the following format:

* * Company name (position) Tel: email: email * *

The implementation code is as follows:

"name = input (" Please enter name: ") company = input (" Please enter name: ") title = input (" Please enter position: ") phone = input (" Please enter phone: ") email = input (" Please enter email: ") print (" * "* 50) print (company) print () print ("% s (% s) "% (name) Title) print () print ("phone:% s"% phone) print ("mailbox:% s"% email) print ("*" * 50) so far I believe you have a deeper understanding of "the basic use of python variables", so you might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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