How to use loop statements in Python?

Python is a high-level programming language that is widely used in fields such as data science, artificial intelligence, web development, and automation. The loop statement is one of the most basic control structures in Python programming, which allows a program to repeatedly execute a block of code until a termination condition is met. In this article we will introduce two types of loop statements in Python - for loop and while loop, and provide some examples to demonstrate their usage.

1. for loop statement

The for loop statement in Python is used to traverse the elements in a sequence or other iterable objects. The format is as follows:

for 元素 in 可迭代对象:
    执行代码块

Among them, the element It is an element taken out from the iterable object, and the execution code block is a piece of code that needs to be executed repeatedly. In each loop, the for loop assigns the next element in the iterable object to the element variable and executes the code block once until all elements in the iterable object have been traversed.

For example, we can use a for loop to print out all the elements in a list:

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

The running result is:

apple
banana
cherry

In addition, we can also use the range() function Generate a sequence of numbers and then iterate through it using a for loop. The range() function can pass a starting value, a ending value and a step parameter to generate an integer sequence. For example:

for i in range(0, 10, 2):
    print(i)

This code will generate an integer sequence from 0 to 9. The step size is 2, and one number is output each time. The result is:

0
2
4
6
8

2. While loop statement

The while loop statement in Python is used to execute repeatedly when a certain condition is met. A code block, the format is as follows:

while 条件:
    执行代码块

Among them, the condition is a Boolean expression, indicating the condition that needs to be met, and the execution code block is a piece of code that needs to be executed repeatedly. In each loop, the while loop checks whether the condition is met, executes the code block once if it is met, and then continues to check the condition until the condition is not met.

For example, we can use a while loop to implement a simple guessing game:

import random

number = random.randint(1, 10)
guess = 0

while guess != number:
    guess = int(input("猜一下数字（1~10）："))
    
    if guess < number:
        print("太小了，请再试一次。")
    elif guess > number:
        print("太大了，请再试一次。")

print("恭喜你，猜对了！")

This code will randomly generate an integer between 1 and 10, and then ask the user to enter a guess number. If the number guessed by the user is not equal to the randomly generated number, the corresponding prompt message is output to allow the user to enter again. If the user guesses correctly, a congratulation message is output and the game ends.

Summary:

Loop statements are an indispensable control structure in Python programming, which can help us repeatedly execute a piece of code until a certain condition is met. In Python, the for loop statement is used to iterate over the elements in a sequence or other iterable object, while the while loop statement is used to repeatedly execute a block of code if a certain condition is met. We need to choose appropriate loop statements and corresponding code implementations based on specific problems, and use them flexibly in actual Python programming.

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