Python variables and operators
variable
1. 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
x = y = z = 0 print(x, y, z)
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
name, age, gender ='Xiao Ming', 25, 'male' print(name, age, gender) x, y, z = 12, 24, 36 print(x, y, z)
2. Reassign
After the variable is re assigned, the latest value in the variable is used when using the variable
score = 100 print(score) score = 90 print(score)
How Python defines and re assigns variables

Python will apply for memory to save data when defining variables. The size of the memory application depends on the size of the saved data

When re assigning a value to a variable, a new memory will be applied. The new memory size is determined by the new data size. Then, the variable will be associated with a new memory, and the original memory will be destroyed automatically
id (variable)  get the memory address corresponding to the variable
num = 100 print(id(num)) num = 200 print(id(num))
Mathematical operator
+ ,, *, / ,%, //, **
Functions as like as two peas in +, , *, / and in mathematics are similar to those in mathematics, x, and functions.
 The result of the division operation is a floating point number
print(10 + 20) print(2  5) print(2 * 5) print(5 / 2) print(4 / 2)
% surplus (mold taking)
x% Y  find the remainder of x divided by y
print(10 % 3) print(15 % 3) print(9 % 2)
Application 1: judge whether there is an integer division relationship between two numbers  judge whether the remainder of two numbers is 0
print(50 % 2) print(25 % 5) print(16 % 3)
Application 2: remove the low digits of integers
 An integer takes the remainder of 10 and can obtain the single digits of this number
 An integer can obtain the last two digits of this number by rounding 100
 An integer can obtain the last three digits of this number by taking the remainder of 1000
num = 26515 print(num % 10) print(num % 100) print(num % 1000)
// divide (round down)
print(5 / 2) # 2.5 print(5 // 2) # 2 print(1.8 // 2) # 0.0 print(5 // 2) # 3
Application scenario: remove the low digits
num = 2342 print(num // 10) print(num // 100) print(num // 1000)
Exercise: get the ten digits of any positive integer
num = 9527 print(num // 10 % 10) print(num %100 // 10) num_1 = 1098 print(num_1 // 10 % 10) print(num_1 % 100 // 10)
Gets the hundreds of any positive integer
num = 28293 print(num // 100 % 10) print(num % 1000 // 100)
** power operation
x**y  find the Y power of x
print(8 ** 3) print(1.3 ** 4) print(9 ** 0.5) print(8 ** (1/3))
Comparison operator
<, > ,==, != ,<=, >=
The result of all comparison operators is Boolean
print(10 > 20) print(10 < 20) print(10 == 20) print(10 != 20) print(10 <= 10) print(10 >= 10)
The comparison operator in Python supports concatenation and represents the range
x = 0.75 print(0 <= x <= 1)
Logical operator
and ,or ,not
1. and
1)Application scenario: it is used when multiple conditions need to be met at the same time, which is equivalent to that in life 2)Operation rule: condition 1 and Condition 2  Both True The result is True，As long as one is False The result is False True and False >True True and True >True False and True >True False and False >False
Exercise: write down the conditions to judge whether a number can be divided by 3 and 7 at the same time
num = 84 print(num % 7 == 0 and num % 3 == 0) print(num % 21 == 0)
Determines whether the specified number is an even number divisible by 3
num = 6 print(num % 3 == 0 and num % 2 == 0) print(num % 6 == 0)
2. or
1)Application scenario: used when multiple conditions are required, as long as one condition is satisfied, which is equivalent to or in life 2)Operation rule: condition 1 or Condition 2  As long as one of the two conditions is True The result is True，Both False The result is when False
Exercise 1: determine whether a number can be divided by 5 or 7
num = 125 print(num % 5 == 0 or num % 7 == 0)
Exercise 2: determine whether the specified year is a leap year
year = 2009 print((year % 4 == 0 and year % 100 != 0) or year % 400 == 0)
3. not
1)Application scenario: (negate a condition) if there are many complex forward write conditions, but the reverse is very simple, the condition Just write it backwards and add it not 2)Operation rules: not condition  Negate condition not True  False not False  True
Exercise: determine whether a number cannot be divided by 3 or 7
num = 90 #Conditional forward write print((num % 7 == 0 and num % 3 != 0) or (num % 7 != 0 and num % 3 == 0) or (num % 7 != 0 and num % != 3)) #Conditional reverse write print(not (num % 7 == 0 and num % 3 == 0))
Logical operator extension
1. Short circuit operation
Condition 1 and Condition 2 and Short circuit: if condition 1 is False，Then the code corresponding to condition 2 will not be executed Condition 1 or Condition 2 or Short circuit: if condition 1 is True，Then the code corresponding to condition 2 will not be executed
2. General operation rules of logical operators
1)and Data 1 and Data 2 2)or Data 1 or Data 2
print(7 and 8) print(7 or 8) print(not 7) print(not 0)
!!! Important conclusion: any type of data in Python can be converted to Boolean values (all have Boolean values), where 0 and null values are False and others are True
print(bool(''), bool(0), bool(0.0), bool(None)) print(bool(8), bool(2), bool(0.34), bool(2.34), bool('ab'), bool(' '))
Assignment Operators
= ,+=, =, *=, /=, %= ,//=, **=
 The assignment operator is not used to calculate a result, but to save the data to a variable
 The left side of all assignment operators must be variables
=: variable = Data
a = 10 a = 100 print(a)
+= ,= ,*=, /= ,%=, //= ,**=
Variable + = Data  add the data saved in the variable and the data after + = and reassign the operation result to the previous variable
Note: for compound assignment operators, the preceding variables must be assigned variables
Emphasis: all assignment operations have no results
a += 10 print(a) # 110 a = 20 print(a) # 90 a %= 4 print(a) #2 a **= 3 print(a)
Operator precedence
Mathematical operators > comparison operators > logical operators > assignment operators (lowest)
In mathematical operators: * * > * > / > / / > >% > + >
(those in brackets shall be counted first)
result = 100 + 2 * 3 ** 2 > 20 * 10  3 print(result)
If Boolean data is involved in mathematical operations, False is 0 and True is 1
result = 100 + (10 > 20) result = 100 + True print(result)