Python3 Operators

What is an operator?

This chapter mainly explains Python's operators.

Let's take a simple example:

4 + 5 = 9

In the example,4and5is calledoperand，+calledoperator。

Python language supports the following types of operators:

• Arithmetic operators
• Comparison (relational) operators
• Assignment operators
• Logical operators
• Bitwise operators
• Membership operators
• Identity operators
• Operator precedence

Next, let's learn Python's operators one by one.

Python Arithmetic Operators

The following assumes variablea=10, variableb=21：

>>> 9//2
4
>>> -9//2
-5

The following example demonstrates the operation of all arithmetic operators in Python:

The above example outputs:

1 - c 的值为： 31
2 - c 的值为： 11
3 - c 的值为： 210
4 - c 的值为： 2.1
5 - c 的值为： 1
6 - c 的值为： 8
7 - c 的值为： 2

Python Comparison Operators

The following assumes variable a is 10 and variable b is 20:

The following example demonstrates the operation of all comparison operators in Python:

The above example outputs:

1 - a 不等于 b
2 - a 不等于 b
3 - a 大于等于 b
4 - a 大于 b
5 - a 小于等于 b
6 - b 大于等于 a

Python Assignment Operators

The following assumes variable a is 10 and variable b is 20:

if (n := len(a)) > 10:
    print(f"List is too long ({n} elements, expected <= 10)")

The following example demonstrates the operation of all assignment operators in Python:

The above example outputs:

1 - c 的值为： 31
2 - c 的值为： 52
3 - c 的值为： 1092
4 - c 的值为： 52.0
5 - c 的值为： 2
6 - c 的值为： 2097152
7 - c 的值为： 99864

In Python 3.8 and later, a new syntax feature called the "Walrus Operator" was introduced, which uses:=symbol. The main purpose of this operator is to perform assignment and return the assigned value simultaneously within an expression.

Using the walrus operator can simplify code in some cases, especially when you need to use the assignment result within an expression. This is useful for simplifying loop conditions or repeated calculations in expressions.

The following is a simple example demonstrating the use of the walrus operator:

• if (n := 10) > 5:: This is using the walrus operator (:=) syntax. The walrus operator performs an assignment operation within an expression.
  • (n := 10): Assigns the variablento 10 and returns the assignment result at the same time.
  • > 5: Checks whether the assignednis greater than 5. If the condition is true, execute the following code block.
• print(n): If the condition is true, print the variablen's value (i.e., 10).

Advantages of the walrus operator:

• The walrus operator (:=) allows assignment within an expression, which can reduce code duplication and improve code readability and conciseness.
• In the above example, the traditional approach requires a separate line to assignn, and thenifstatement for condition checking. With the walrus operator, the code canifdirectly perform assignment and condition checking within the statement.

Python Bitwise Operators

Bitwise operators treat numbers as binary for calculation. The bitwise operation rules in Python are as follows:

In the table below, variable a is 60 and b is 13. The binary formats are as follows:

a = 0011 1100

b = 0000 1101

-----------------

a&b = 0000 1100

a|b = 0011 1101

a^b = 0011 0001

~a  = 1100 0011

The following examples demonstrate the operations of all Python bitwise operators:

The output of the above example is:

1 - c 的值为： 12
2 - c 的值为： 61
3 - c 的值为： 49
4 - c 的值为： -61
5 - c 的值为： 240
6 - c 的值为： 15

Python Logical Operators

Python language supports logical operators. The following assumes variable a is 10 and b is 20:

The output of the above example is:

The output of the above example is:

1 - 变量 a 和 b 都为 true
2 - 变量 a 和 b 都为 true，或其中一个变量为 true
3 - 变量 a 和 b 有一个不为 true
4 - 变量 a 和 b 都为 true，或其中一个变量为 true
5 - 变量 a 和 b 都为 false，或其中一个变量为 false

Python Membership Operators

In addition to the operators above, Python also supports membership operators. The test instance contains a series of members, including strings, lists, or tuples.

The following examples demonstrate the operations of all Python membership operators:

The output of the above example is:

1 - 变量 a 不在给定的列表中 list 中
2 - 变量 b 不在给定的列表中 list 中
3 - 变量 a 在给定的列表中 list 中

Python Identity Operators

Identity operators are used to compare the memory locations of two objects.

Note: id()The function is used to obtain the memory address of an object.

The following examples demonstrate the operations of all Python identity operators:

The output of the above example is:

1 - a 和 b 有相同的标识
2 - a 和 b 有相同的标识
3 - a 和 b 没有相同的标识
4 - a 和 b 没有相同的标识

The difference between is and ==:

is is used to determine whether two variables reference the same object; == is used to determine whether the values of the referenced variables are equal.

>>>a = [1, 2, 3] >>> b = a >>> b is a True >>> b == a True >>> b = a[:] >>> b is a False >>> b == a True

Python Operator Precedence

The following table lists all operators from highest to lowest precedence. Operators in the same cell have the same precedence. Operators refer to binary operations unless otherwise specified. Operators in the same cell are grouped from left to right (except for exponentiation, which is grouped from right to left):

The following examples demonstrate the operations of all Python operator precedence:

The output of the above example is:

(a + b) * c / d 运算结果为： 90.0
((a + b) * c) / d 运算结果为： 90.0
(a + b) * (c / d) 运算结果为： 90.0
a + (b * c) / d 运算结果为： 50.0

and has higher precedence:

The above example first evaluatesy and zand returns False, thenx or Falsereturns True, and the output result is:

情况1：默认优先级（先算and）
yes

情况2：强制改变优先级（先算or）
no

Note:Python3 no longer supports<>operator, you can use!=instead, if you really need to use this comparison operator, you can use the following method:

>>> from __future__ import barry_as_FLUFL
>>> 1 <> 2
True

x = True
y = False
z = False

if x or y and z:
    print("yes")
else:
    print("no")

x = True
y = False
z = False

if not x or y:
    print(1)
elif not x or not y and z:
    print(2)
elif not x or y or not y and x:
    print(3)
else:
    print(4)