Day3 data types and operators summary and job

Today's summary

One 、 Variable

1、 Variable ： It is a kind of container specially used to store data （ Variables are used to hold data , After saving the data , Using variables

Is to use the data stored in the variable ）

grammar ：

Variable name = data

explain ：

1） Variable name — Named by the programmer himself

​ requirement ：a. Is an identifier.

​ b. It can't be a keyword

​ standard ：a. Know what you know ( When you see the variable name, you know what data is stored in the variable )

​ b. Do not use the system function name (print、input、type)、 Class name (int、float、…) And the module name c. The letters are all lowercase ,

Multiple words are separated by underscores

2）= - Assignment symbol ; Fixed writing

3） data - It can be any expression with a result , such as ： A specific data 、 Calculation results 、 Variables that have been assigned 、 function

Call expressions, etc

2、 Define multiple variables at the same time

1） Define multiple variables at the same time and assign the same value : Variable name 1 = Variable name 2 = Variable name 3 = … = data

a1 = a2 = a3 = 100

2） Define multiple variables at the same time and assign different values : Variable name 1, Variable name 2, Variable name 3, … = data 1, data 2, data 3, …

The number of the preceding variables must be consistent with the number of the following data

b1, b2 = 10, 20

3、python The principle of defining variables and reassigning variables

python The variable is defined by applying for memory first , The size of the memory application depends on the size of the data to be saved ;

When reassigning , Will reapply for new memory , The size of the new memory depends on the size of the new data .

id( Variable ) - Gets the address of the data in the variable

Two 、 Mathematical operators

1、 Add, subtract, multiply and divide

python The addition, subtraction, multiplication and division in is the same as in mathematics

Be careful ：/ The result of the operation must be float; +、-、* The type of operation result depends on whether there are floating-point numbers in the operation object

2、 Remainder ( modulus ) - %

Remainder is the remainder in mathematics

The rules ： x % y – seek x Divide y The remainder of

Application scenarios 1： Judge whether there is an integer division relationship between two numbers - Judge whether the remainder of two numbers is 0

Application scenarios 2： Take the lower digits - Yes 10 perhaps 10 Of N Secondary surplus

3、 to be divisible by - //

function ： Seeking quotient , Quotient rounding off

Application scenarios 1: Get the quotient of an integer if it can be divided by an integer

Application scenarios 2： Remove the lower digits of an integer - to be divisible by 10 perhaps 10 Of N The next power

4、 Power operation -**
The rules ： x ** y - seek x Of y Power

3、 ... and 、 Comparison operator

Comparison operator ：>( Greater than )、<( Less than )、==( be equal to )、>=( Greater than or equal to )、<=( Less than or equal to )、!=( It's not equal to )

Be careful 1： The result of all comparison operators is Boolean

Be careful 2：python The comparison operators in can be concatenated to represent the range like mathematics

Four 、 Logical operators

1、 Logic and - and

Application scenarios ： Equivalent to... In life ’ also ’, It is used to connect two conditions that are true at the same time

Operator rule ： Conditions 1 and Conditions 2 - All two are True The result is True, As long as one is False The result is False

True and True - True

True and False - False

False and True - False

False and False - False

2、 Logic or - or

Application scenarios ： Equivalent to... In life ’ perhaps ’; If two or more conditions are required, as long as one condition is satisfied , So take these

Conditional use or Connect

Operational rules ： Conditions 1 or Conditions 2 - All two are False The result is False, As long as one is True The result is True

True or True - True

True or False - True

False or True - True

False or False - False

3、 Logic is not - not

Application scenarios ： Deny a condition ; If a condition is written forward, the situation is very complicated , The reverse is simple , Then we will

Condition reverse write plus not

Operational rules ：not Conditions - Negate the specified condition

not True - False

not False - True

5、 ... and 、 Assignment operator

Assignment operator ：=、+=、-=、*=、/=、%=、//=、**=

Conclusion ： The function of all assignment operators is to store data in variables

1、=

Variable name = data - take = The data on the right is assigned to the variable on the left ( Variable names can be defined , It can also be undefined )

2、 +=

Variable name += data - Take out the data saved in the variable and add it with the following data , Reassign the result of the operation to the variable

( Variable names must be defined )

3、 Operator precedence

Mathematical operators > Comparison operator > Logical operators > Assignment operator ( The minimum )

** > *、/、%、// > +、-

If there are brackets, count them first

day3 Data types and Operator jobs

choice question

1. print(100 - 25 * 3 % 4) What should be output ? （B）

   A. 1
   

   B. 97
   

   C. 25
   

   D. 0
   

2. Which of the following statements is wrong （D）.

   A. Except for dictionary types , All standard objects can be used for Boolean testing
   

   B. The Boolean value of an empty string is False
   

   C. The Boolean value of an empty list object is False
   

   D. The value is 0 The Boolean value of any numeric object of is False
   

3. Python Unsupported data types are （A）.

   A. char
   

   B. int
   

   C. float
   

   D. list
   

4. （ multi-select ）n = 6784, You can get 7 The way to do this is （CD）.

   A. n / 1000 % 100
   

   B. n % 1000 / 100
   

   C. n // 100 % 10
   

   D. n // 10 % 100 // 10
   

5. Run the following program , When entering... From the keyboard 12, The result of the operation is （A）.

   x = (input())
   print(type(x))
   

   A. <class 'str'>
   

   B. <class 'int'>
   

   C. error
   

   D. class 'dict'
   

6. The operation result of the following expression is ( D ) .

   a = 100
   b = False
   print(a * b > -1)
   

   A. False
   

   B. 1
   

   C. 0
   

   D.True
   

Completion

1. stay Python The empty type is （None）.

2. The function name to view the type of data in the variable is （type）.

3. It is known that x = 3 == 3, After execution , Variable x The value of is （True）.

4. It is known that x = 3, Then execute the statement x += 6 after ,x The value of is （9）.

5. expression 3 ** 2 The value of is （9）, expression 3 * 2 The value of is （6）, expression 4 ** 0.5 The value of is （2）.

Programming questions

1. Write to determine whether a number can be simultaneously 3 and 7 Divisible conditional statement , And print the corresponding results .

    for example ： Input  21  Print  True,  Input  9  Print  False.
   num = int(input(' Please enter a number ：'))
   print(num % 3 == 0 and num % 7 == 0)
   

2. Write to determine whether a number can be 3 perhaps 7 to be divisible by , But not both 3 perhaps 7 Divisible conditional statement , And print the corresponding results .

    for example ： Input  14  Print  True,  Input  4  Print  False,  Input  21  Print  False.
   num = int(input(' Please enter a number ：'))
   print((num % 3 == 0 or num % 7 == 0) and (not(num % 3 == 0 and num % 7 == 0) ))
   

3. Enter year , Write code to judge whether the entered year is a leap year , And print the corresponding results .( It's a leap year condition : Can be 4 Divisible but not by 100 Divisible or capable of being divisible by 400 Divisible year )

    for example ： Input  2020  Print  True,  Input  2011  Print  False
   year = int(input(' Please enter the year ：'))
   print((year % 4 == 0 and year % 100 != 0) or (year % 400 == 0))
   

4. Suppose today's class time is 15678 second , Programming to calculate the class time today is how many hours , How many minutes? , How many seconds ; With ‘XX when XX branch XX second ’ It's expressed in a different way .

    for example :  Time  67  second   —> 0  when  1  branch  7  second 
   time = int(input(' Please enter the time ：'))
   hour = time // 3600
   minute = time % 3600 // 60
   second = time % 3600 % 60
   print(hour,' when ',minute,' branch ',second,' second ',sep = '')
   

5. Define two variables to save a person's height and weight , Programming to determine whether the person's body is normal !

   The formula : weight (kg)/ height (m) The square value of stay 18.5 ~ 24.9 It's normal .

    for example :  Enter the weight : 55,  Enter the height ：1.55,  Output : True
   height = float(input(' Please enter height ：'))
   weight = int(input(' Please enter the weight ：'))
   index = weight / (height ** 2)
   print( 18.5 <= index <= 24.9)
   

Short answer

1. Python What are the built-in data types ?

   integer （int)、 floating-point (float)、 Boolean (bool)、 Null value (None)、 Character (str).

2. Write your thoughts about today ⽇ Where there are questions in the teaching content of the day ⽅ Fang ( Or knowledge points that feel difficult ).

   nothing