Python not and order

What is operator precedence in Python?

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Overview

Operator precedence in Python simply refers to the order of operations. Operators are used to perform operations on variables and values.

Python classifies its operators in the following groups:

• Arithmetic operators
• Assignment operators
• Comparison operators
• Logical/Bitwise operators
• Identity operators
• Membership operators

Arithmetic Operators

Common arithmetic operators in Python include:

• Addition +
• Subtraction —
• Multiplication *
• Division/modulus / or //
• Exponentiation **
• Brackets/Parenthesis ()

Order of operations

The order of operations of the arithmetic operators can be remembered using the acronym BEDMAS.

The acronym stands for the following words, which tell us which operator comes first:

• B= Bracket
• E = Exponentiation
• D = Division
• M = Multiplication
• A = Addition
• S = Subtraction

Through the acronym, we can see that the bracket/parenthesis operator comes before the exponentiation operation in Python, according to the order of operations.

The same logic applies to each of the following operators, down to the subtraction operator.

Example

To fully grasp BEDMAS and the order of preference of the operators, let’s take a look at the example below:

From this program, we can see that there are three operators:

According to operator precedence, Python first deals with the numbers in the bracket operator (B): (5 + 3) = 8 .

We then proceed to the exponentiation operator (E): 2 ** 2 = 4 .

Finally, the results of both the bracket ( 8 ) and exponentiation ( 4 ) operators are then executed using the multiplication operator (M): 8 * 4 = 32 .

In short, Python followed the order of operators outlined in BEDMAS.

Example

The same logic applies to the examples below:

x = 3 + 8 * 2** 3
print(x)
y= (4 * 2) + 6 / 3 - 2
print(y)

The value of x in the example above follows E,M,A order of operations while the value of y follows B,D,S order.

Assignment Operators

Common assignment operators in Python include:

• Assign operator =
• Add AND operator +=
• Subtract AND operator -=
• Multiply AND operator *=
• Divide AND operator /=
• Modulo AND operator %=
• Exponent AND operator **=

Order of operation

Since these operators are not associative, there is no order of operation for them. They are always performed or declared exclusively.

Example

# using the assigm operator
 
x = 6
y = 2
 
# to generate the Add AND operator i.e x + y = 8
x += y
print(x)
 
# to generate the subtract AND operator i.e x - y = 8 - 2 = 6
 
x -= y
 
print(x)
# to generate the multiply AND ooperator i.e x * y = 6 * 2 = 12
x *= y
 
print(x)
# to generate the divide AND operator i.e x / 2 = 12 / 2 = 6
 
x /= y
 
print(x)
# to generate the modulo AND operator 1.e x %= 2 = 6 % 2 = 0
x %= y
print(x)
 

Comparison Operators

Comparison operators include:

• Equal to ==
• Not equal to !=
• Greater than >
• Less than
• Greater than or equal to >=
• Less than or equal to

Order of operation

Since these operators are not associative, there is no order of operation for them. They are always performed or declared exclusively.

Example

The program below introduces each of the comparison operators:

x = 6
 
y = 2
 
if x == y:
 
print('x is equal to y')
 
else:
 
print('x is not equal to y')
 
if x != y:
 
print('x is not equal to y')
 
else:
 
print('x is equal to y')
 
if x > y:
 
print('x is greater than y')
 
else:
 
print('x is not greater thab y')
 
if x < y:
 
print('x is less than y')
 
else:
 
print('x is not less than y')
 
if x >= y:
 
print('x is greater than or equal to y')
 
else:
 
print('x is not greater than or equal to y')
 
if x  
print('x is less than or equal to y')
 
else:
 
print('x is not less than or equal to y')

Logical operators

Logical operators in Python include:

Order of operations

The order of operations for logical operators from the highest to the lowest is as follows:

# Precedence of 'or' & 'and'
name = "Theophilus"
age = 0
 
if name == "Theophilus" or name == "John" and age >= 2 :
 
print("Hello! Welcome.")
else :
 
print("Good Bye!!")

The example above shows how the precedence of the logical and is greater than the logical or .

Identity operators

The identity operators in Python include:

The order of precedence of the identity operators in Python from left to right would be: is and is not .

Membership operators

The order of precedence of the membership operators in Python from left to right is in , not in .

Example

In the code below, we check whether or not the values of x = 2 and y = 4 are available in list by using in and not in operators.

x = 2
y = 4
list = [1, 2, 3, 6, 7 ];
if ( x in list ):
 
print("Yes x is in the list")
else:
 
print("x can not be found on the list")
if ( y not in list ):
 
print("y is not in the given list")
else:
 
print("y is in the given list")

The example above shows how the precedence of in is greater than the not in .

Summary

The table below shows the summary of the different operator and their precedencies in python

Operators	Examples	Operator Precedence(from left to right)
Arithmetic operators	Addition + , Subtraction — , Multiplication * , Division/modulo / or // ,Exponential ** , Bracket ()	() , ** , / or // , * , + , —
Assignment operators	Assign operator = , Add AND operator += , Subtract AND operator -= , Multiply AND operator *= , Divide AND operator /= , Modulo AND operator %= , Exponent AND operator **=	No order of operation
Comparison operators	equal to == , not equal to != , greater than > , less than < , greater than or equal to >= , less than or equal to	No order of operation
Logical operators	Logical AND, Logical OR, Logical NOT	NOT, AND, OR
Identity operators	Is, Is not	Is, Is not
Membership operators	in, not in	in, not in

Источник

№29 Приоритетность и ассоциативность операторов / для начинающих

В этом материале рассмотрим приоритетность и ассоциативность операторов в Python. Тема очень важна для понимания семантики операторов Python.

После прочтения вы должны понимать, как Python определяет порядок исполнения операторов. У некоторых из них более высокий уровень приоритета. Например, оператор умножения более приоритетный по сравнению с операторами сложения или вычитания.

В выражении интерпретатор Python выполняет операторы с более высоким уровнем приоритета первыми. И за исключением оператора возведения в степень ( ** ) они выполняются слева направо.

Приоритетность операторов в Python

Как работает приоритетность операторов в Python?

Выражение — это процесс группировки наборов значений, переменных, операторов и вызовов функций. При исполнении таких выражений интерпретатор Python выполняет их.

Здесь «3 + 4» — это выражение Python. Оно содержит один оператор и пару операндов. Но в более сложных инструкциях операторов может быть и несколько.

Для их выполнения Python руководствуется правилом приоритетности. Оно указывает на порядок операторов.

Примеры приоритетов операторов

В следующих примерах в сложных выражениях объединены по несколько операторов.

 
# Сначала выполняется умножение 
# потом операция сложения 
# Результат: 17 
5 + 4 * 3 
 
Однако порядок исполнения можно поменять с помощью скобок (). Они переопределяют приоритетность арифметический операций.
 
 
# Круглые скобки () переопределяют приоритет арифметических операторов 
# Вывод: 27 
(5 + 4) * 3 
 
Следующая таблица демонстрирует приоритетность операторов от высокой до самой низкой.
 
 
 
Операторы
 
Применение
 
  
 
 
 
Скобки (объединение)
 
 
 
f(args…)
 
Вызов функции
 
 
 
x[index:index]
 
Срез
 
 
 
x[index]
 
Получение по индексу
 
 
 
x.attribute
 
Ссылка на атрибут
 
 
 
**
 
Возведение в степень
 
 
 
~x
 
Побитовое нет
 
 
 
+x, -x
 
Положительное, отрицательное число
 
 
 
*, /, %
 
Умножение, деление, остаток
 
 
 
+, —
 
Сложение, вычитание
 
 
 
>
 
Сдвиг влево/вправо
 
 
 
&
 
Побитовое И
 
 
 
^
 
Побитовое ИЛИ НЕ
 
 
 
|
 
Побитовое ИЛИ
 
 
 
in, not in, is, is not, , >=, <>, !=, ==
 
Сравнение, принадлежность, тождественность
 
 
 
not x
 
Булево НЕ
 
 
 
and
 
Булево И
 
 
 
or
 
Булево ИЛИ
 
 
 
lambda
 
Лямбда-выражение
 
 
 
 
Ассоциативность операторов
 
В таблице выше можно увидеть, что некоторые группы включают по несколько операторов python. Это значит, что все представители одной группы имеют один уровень приоритетности.
 
При наличии двух или более операторов с одинаковым уровнем в дело вступает ассоциативность, определяющая порядок.
 
Что такое ассоциативность в Python?
 
Ассоциативность — это порядок, в котором Python выполняет выражения, включающие несколько операторов одного уровня приоритетности. Большая часть из них (за исключением оператора возведения в степень ** ) поддерживают ассоциативность слева направо.
 
Примеры
 
Например, у операторов умножения и деления приоритетность одинаковая. В одном выражении тот, что находится слева, будет выполняться первым.
 
Источник
 
Precedence and Associativity of Operators in Python
 
The combination of values, variables, operators, and function calls is termed as an expression. The Python interpreter can evaluate a valid expression.
 
Here 5 - 7 is an expression. There can be more than one operator in an expression.
 
To evaluate these types of expressions there is a rule of precedence in Python. It guides the order in which these operations are carried out.
 
For example, multiplication has higher precedence than subtraction.
 
# Multiplication has higher precedence # than subtraction >>> 10 - 4 * 2 2
 
But we can change this order using parentheses () as it has higher precedence than multiplication.
 
# Parentheses () has higher precedence >>> (10 - 4) * 2 12
 
The operator precedence in Python is listed in the following table. It is in descending order (upper group has higher precedence than the lower ones).
 
 
 
 
Operators
 
Meaning
 
 
 
()
 
Parentheses
 
 
 
**
 
Exponent
 
 
 
+x , -x , ~x
 
Unary plus, Unary minus, Bitwise NOT
 
 
 
* , / , // , %
 
Multiplication, Division, Floor division, Modulus
 
 
 
+ , -
 
Addition, Subtraction
 
 
 
>
 
Bitwise shift operators
 
 
 
&
 
Bitwise AND
 
 
 
^
 
Bitwise XOR
 
 
 
|
 
Bitwise OR
 
 
 
== , != , > , >= , < , 
Comparisons, Identity, Membership operators
 
 
 
not
 
Logical NOT
 
 
 
and
 
Logical AND
 
 
 
or
 
Logical OR
 
 
 
 
Let's look at some examples:
 
Suppose we're constructing an if. else block which runs if when lunch is either fruit or sandwich and only if money is more than or equal to 2 .
 
# Precedence of or & and meal = "fruit" money = 0 if meal == "fruit" or meal == "sandwich" and money >= 2: print("Lunch being delivered") else: print("Can't deliver lunch")
 
This program runs if block even when money is 0 . It does not give us the desired output since the precedence of and is higher than or .
 
We can get the desired output by using parenthesis () in the following way:
 
# Precedence of or & and meal = "fruit" money = 0 if (meal == "fruit" or meal == "sandwich") and money >= 2: print("Lunch being delivered") else: print("Can't deliver lunch")
 
Associativity of Python Operators
 
We can see in the above table that more than one operator exists in the same group. These operators have the same precedence.
 
When two operators have the same precedence, associativity helps to determine the order of operations.
 
Associativity is the order in which an expression is evaluated that has multiple operators of the same precedence. Almost all the operators have left-to-right associativity.
 
For example, multiplication and floor division have the same precedence. Hence, if both of them are present in an expression, the left one is evaluated first.
 
# Left-right associativity # Output: 3 print(5 * 2 // 3) # Shows left-right associativity # Output: 0 print(5 * (2 // 3))
 
Note: Exponent operator ** has right-to-left associativity in Python.
 
# Shows the right-left associativity of ** # Output: 512, Since 2**(3**2) = 2**9 print(2 ** 3 ** 2) # If 2 needs to be exponated fisrt, need to use () # Output: 64 print((2 ** 3) ** 2)
 
We can see that 2 ** 3 ** 2 is equivalent to 2 ** (3 ** 2) .
 
Non associative operators
 
Some operators like assignment operators and comparison operators do not have associativity in Python. There are separate rules for sequences of this kind of operator and cannot be expressed as associativity.
 
Furthermore, while chaining of assignments like x = y = z = 1 is perfectly valid, x = y = z+= 2 will result in error.
 
# Initialize x, y, z x = y = z = 1 # Expression is invalid # (Non-associative operators) # SyntaxError: invalid syntax x = y = z+= 2
 
 File "", line 8 x = y = z+= 2 ^ SyntaxError: invalid syntax
 
Table of Contents
 
Источник
 
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