Python learning notes (3): operators and expressions

1. Operators

Operator	Name	Description	Example
+	Add	Add two objects	3 + 5 get 8. "A" + "B" get "AB ".
-	Subtraction	Returns a negative number or a number minus another number.	-5.2 returns a negative number. 50-24 get 26.
*	Multiplication	Returns a string that is repeated several times.	2*3 get 6. "La" * 3 get "lalala ".
**	Power	Returns the Power Y of X.	3 ** 4 get 81 (3*3*3*3 ).
/	Division	X divided by Y	4/3 to get 1 (integer division to get the integer result ). 4.0/3 or 4/3.0 get 1.3333333333333333
//	Integer Remainder	Returns the integer part of the operator.	4 // 3.0 get 1.0
%	Modulo	Returns the remainder of the Division.	8/3 get 2. -25.5% 2.25 get 1.5
<	Move left	Shifts a certain number of BITs to the left (each number is expressed as a bit or binary number in the memory, that is, 0 or 1)	2 <2 get 8. -- 2 indicates 10 in bits
>	Right Shift	Shifts a certain number of BITs to the right.	11> 1 to get 5. -- 11 is expressed as 1011 in bits. After moving 1 bit to the right, 101 is obtained, that is, 5 in decimal format.
&	Bitwise AND	Bitwise AND	5 & 3 get 1
|	By bit or	Number by bit or	5 | 3 get 7
^	Bitwise OR	Bitwise OR	5 ^ 3 get 6
~	Flip by bit	The bitwise flip of X is-(x + 1)	~ 5 get-6
<	Less	Returns whether X is less than Y. All comparison operators return 1 to indicate true, and 0 to indicate false. This is equivalent to the special variables true and false. Note: These variable names are capitalized.	5 <3 returns 0 (false) and 3 <5 returns 1 (true ). Comparison can be connected at any time: 3 <5 <7 returns true.
>	Greater	Returns whether X is greater than Y.	5> 3 return true. If both operands are numbers, they are first converted to a common type. Otherwise, it always returns false.
<=	Less than or equal	Returns whether X is less than or equal to y.	X = 3; y = 6; x <= y returns true.
> =	Greater than or equal	Returns whether X is greater than or equal to y.	X = 4; y = 3; x> = y returns true.
=	Equal	Equal comparison object	X = 2; y = 2; X = y returns true. X = "str"; y = "str"; X = y returns false. X = "str"; y = "str"; X = y returns true.
! =	Not equal	Compare whether two objects are not equal	X = 2; y = 3; X! = Y returns true.
Not	Boolean "Non"	If X is true, false is returned. Returns true if X is false.	X = true; not X returns false.
And	Boolean and	If X is false, X and Y returns false. Otherwise, it returns the calculated value of Y.	X = false; y = true; X and Y, returns false because X is false. Python does not calculate y here, because it knows that the value of this expression must be false (because X is false ). This phenomenon is called short circuit computation.
Or	Boolean OR	If X is true, X or Y returns true, otherwise it returns the calculated value of Y.	X = true; y = false; X or Y returns true. Short circuit calculation is also applicable here.

2. Operator priority

The following table operators are from the lowest to the highest. Python first calculates the bottom operators in the table, and then calculates the top operators in the table. In fact, we strongly recommend that you use parentheses to group operators and operands so as to clearly point out the order of operations and achieve easy read.

Calculation order: it is determined by the operator priority by default. If you want to change their order, use parentheses, for example: (2 + 3) * 4

Combination rules: operators are combined from left to right (operators of the same level). For example, 2 + 3 + 4 is calculated as (2 + 3) + 4.

The value assignment operator is combined by the right to the left, for example, a = B = C is processed as a = (B = C)

Operator	Description
Lambda	Lambda expressions
Or	Boolean OR
And	Boolean and
Not x	Boolean "Non"
In, not in	Member Testing
Is, is not	Identity Test
<, <=,>, >= ,! =, =	Comparison
|	By bit or
^	Bitwise OR
&	Bitwise AND
<,>	Shift
+ ,-	Addition and subtraction
*,/, %	Multiplication, division, and remainder
+ X,-x	Plus or minus sign
~ X	Flip by bit
**	Index
X. Attribute	Attribute reference
X [Index]	Subscript
X [index: Index]	Addressing segment
F (arguments ...)	Function call
(Expression ,...)	Bind or display tuples
[Expression,...]	List display
{Key: datum ,...}	Dictionary display
'Expression ,...'	String Conversion

3. Expression

# This is a simple expression example code # filename: expression. pylength = 5 breadth = 2 area = length * breadthprint ("area is", Area) print ("Perimeter is", 2 * (Length + breadth ))

The output result is as follows:

Area is 10

Perimeter is 14