A Byte of Python notes (3), bytepython

A Byte of Python notes (3), bytepython

Chapter 3 operators and expressions

Most statements (logical rows) contain expressions. Example: 2 + 3. An expression can be divided into operators and operands.

 

Operator

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 to get 'lala '.
**	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 Division	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 and 1)	2 <2 get 8. -- 2 expressed in BITs as 10
>	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 to 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, False is returned. 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 y 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; 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, it 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.

 

Operator priority

The following table lists the operator priorities of Python, from the lowest (loose combination) to the highest (most closely combined ). This means that in an expression, Python will first calculate the following operators in the table, and then calculate the operators listed in the upper part of the table.

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
(Experession ,...)	Bind or display tuples
[Expression,...]	List display
{Key: datum ,...}	Dictionary display
'Expression ,...'	String Conversion

 

Calculation Order: The operator priority table determines which operator is computed before another operator. You can use parentheses to change the order of calculation.

Combination rules: Usually from left to right, and the value assignment operator from right to left.

 

Expression

Calculates the area and perimeter of a rectangle.

# !/usr/bin/python# Filename: expression.pylength = 5breadth = 2area = length * breadthprint 'Area is', areaprint 'Perimeter is %d' % (2*(length + breadth))

Output

 

Note the two print modes of print.