How to use conditional statements in Python?

Conditional statements in the Python language are an important programming concept that are often used to control the flow of the program and determine whether to perform different operations under different circumstances. In Python, commonly used conditional statements include if statements and if-else statements. This article will introduce how to use conditional statements in Python.

1. Basic usage of if statement
The if statement is one of the most commonly used conditional statements in Python. It is used to execute a block of code under specific conditions. The basic syntax is as follows:

if condition:

# 执行当条件为真时执行的代码块

where condition is a Python expression, which can be a comparison statement, logical operator or other expression that can return a Boolean value . When condition is true, the subsequent code block is executed, otherwise the code block is skipped.

The following is a simple example:

x = 10
if x > 5:
    print("x > 5")

In this example, the condition x > 5 is true, so the print statement is executed and x > 5 is output. Note that in Python, code blocks are implemented by indentation, so the code block after the if statement must be indented.

2. How to use the if-else statement
The if statement can only judge one condition. If you need to execute different code blocks under different circumstances, you can use the if-else statement. The basic syntax is as follows:

if condition:

# 执行当条件为真时执行的代码块

else:

# 执行当条件为假时执行的代码块

The else statement can be omitted. The code block after the if statement is executed when the condition is true, otherwise the code block after the else statement is executed.

The following is an example:

x = 10
if x > 15:
    print("x > 15")
else:
    print("x <= 15")

In this example, because x > 15 is not true, the code block after the else statement is executed and x <= 15 is output.

3. How to use the if-elif-else statement
If you need to execute different code blocks under multiple conditions, you can use the if-elif-else statement. The basic syntax is as follows:

if condition1:

# 执行当条件1为真时执行的代码块

elif condition2:

# 执行当条件2为真时执行的代码块

...
else:

# 执行当以上条件均不成立时执行的代码块

Among them, the elif statement There can be multiple, and the else statement can be omitted. When condition 1 is met, the code block after the if statement is executed. Otherwise, condition 2 is checked. If it is met, the code block after the elif statement is executed, and so on, until a code block that satisfies the condition is found. Otherwise, the code block after the else statement is executed. .

The following is an example:

x = 10
if x > 15:
    print("x > 15")
elif x > 5:
    print("5 < x <= 15")
else:
    print("x <= 5")

In this example, because x <= 15 and x > 5 is true, the code block after the elif statement is executed and 5 < x is output. <= 15.

4. Nested conditional statements
In Python, conditional statements can be nested. In other words, one or more if statements can be nested within an if statement to implement more complex logic.

The following is a sample code:

x = 10
y = 5
if x > 5:
    if y > 3:
        print("x > 5 and y > 3")
    else:
        print("x > 5 and y <= 3")
else:
    print("x <= 5")

In this example, if x > 5, the first if statement will be executed, and then it will be judged whether y is greater than 3, and if it is true, it will output " x > 5 and y > 3", otherwise output "x > 5 and y <= 3". If x <= 5, then output "x <= 5".

Conclusion:
This article introduces the basic syntax and usage of conditional statements in Python, including if statements, if-else statements, if-elif-else statements and nested conditional statements. Conditional statements in Python can make the program run more flexibly and smoothly. They are often used to control the flow of the program and determine how to perform different operations under different circumstances.

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