Detailed explanation of techniques and precautions for Python flow control statements

Tips and precautions for using Python flow control statements

As a high-level programming language, Python flow control statements are an important tool for realizing program logic. Mastering the use of flow control statements can improve the readability and efficiency of the code. This article will introduce the usage skills of Python's commonly used flow control statements if, for and while, and provide corresponding code examples.

1. If statement

The if statement is one of the most commonly used flow control statements in Python, which is used to execute different code blocks based on conditional judgments.

1. Single condition judgment

Grammar format:

if 条件:
    代码块

Sample code:

score = 90
if score >= 60:
    print("及格了")

Output result:

及格了

2. Multiple condition judgments

Grammar format:

if 条件1:
    代码块1
elif 条件2:
    代码块2
else:
    代码块3

Sample code:

score = 85
if score >= 90:
    print("优秀")
elif score >= 80:
    print("良好")
elif score >= 60:
    print("及格")
else:
    print("不及格")

Output result:

良好

2. for Loop statement

The for loop statement is an important tool in Python for traversing sequence objects such as lists, tuples, and strings.

1. Traverse the list

Syntax format:

for 变量 in 列表:
    代码块

Sample code:

fruits = ['apple', 'banana', 'orange']
for fruit in fruits:
    print(fruit)

Output result:

apple
banana
orange

2. Traverse the dictionary

Grammar format:

for 键, 值 in 字典.items():
    代码块

Sample code:

person = {'name': '张三', 'age': 20, 'gender': '男'}
for key, value in person.items():
    print(key, value)

Output result:

name 张三
age 20
gender 男

3. while loop statement

The while loop statement is an important tool in Python for looping blocks of code. It decides whether to continue executing the loop based on whether the condition is met.

Grammar format:

while 条件:
    代码块

Sample code:

count = 0
while count < 5:
    print(count)
    count += 1

Output result:

0
1
2
3
4

4. Precautions

1. Usage Colon (:): A colon is required after the flow control statement in Python to indicate the beginning of the code block.
2. Indented code blocks: Python uses indentation to represent code blocks. The indentation amount of code blocks at the same level must be the same.
3. Pay attention to the loop condition: If the loop condition is always True, it may cause an infinite loop. You need to use the break statement in the loop to interrupt the loop.
4. Pay attention to the order of condition judgment: When judging multiple conditions, pay attention to the order of conditions, and judge the more special or important conditions first.

Summary:

This article introduces the usage skills of Python flow control statements if, for and while, and gives corresponding code examples. I hope that by studying this article, readers can master the usage of Python flow control statements and improve the efficiency and readability of the code. At the same time, when using flow control statements, you must also pay attention to the indentation of the code, the order of condition judgments, and the judgment of loop conditions to ensure the correct execution of the program.

Reference materials:
Python official documentation: https://docs.python.org/3/tutorial/controlflow.html

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