Python编程笔记（python编程入门与案例详解）

1. Python简介Python是一种解释型、高级和通用的编程语言。它通过显著的缩进使用来强调代码的可读性。

# Hello World program
print("Hello, World!")

2.变量和数据类型变量用于存储数据值。Python支持各种数据类型，如整数、浮点数、字符串等。

# Variables and data types
x = 10        # Integer
y = 3.14      # Float
name = "Alice"  # String
is_valid = True  # Boolean
print(x, y, name, is_valid)

3.条件语句条件语句允许基于条件执行代码。

# Conditional statements
age = 18
if age >= 18:
    print("You are an adult.")
else:
    print("You are a minor.")

4.循环Python提供for和while循环来迭代序列或重复操作。

示例（for循环）：

# For loop example
for i in range(5):
    print(i)

例如（while循环）：

# While loop example
count = 0
while count < 5:
    print(count)
    count += 1

5.函数函数是执行特定任务的可重用代码块。

# Function example
def greet(name):
    return f"Hello, {name}!"
print(greet("Alice"))

6.列表和字典列表用于在单个变量中存储多个项，字典以键值对的形式存储数据。

示例（列表）：

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

示例（字典）：

# Dictionary example
person = {"name": "Alice", "age": 25}
print(person["name"], person["age"])

7. Python允许你读写文件。

范例：

# File handling example
with open("example.txt", "w") as file:
    file.write("Hello, File!")
with open("example.txt", "r") as file:
    content = file.read()
    print(content)

8.异常处理使用try、except和finally块优雅地处理错误。

# Exception handling example
try:
    num = int(input("Enter a number: "))
    print(10 / num)
except ValueError:
    print("Invalid input! Please enter a number.")
except ZeroDivisionError:
    print("Cannot divide by zero.")
finally:
    print("Execution complete.")

9. Python支持使用类和对象进行面向对象编程。

# Class and object example
class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def introduce(self):
        return f"My name is {self.name} and I am {self.age} years old."
person1 = Person("Alice", 25)
print(person1.introduce())

10.库和模块Python拥有丰富的库生态系统，可用于各种任务。

# Using the math module
import math
print(math.sqrt(16))  # Square root
print(math.pi)        # Value of Pi

实时示例：网页搜罗

# Web scraping using requests and BeautifulSoup
import requests
from bs4 import BeautifulSoup
url = "https://example.com"
response = requests.get(url)
soup = BeautifulSoup(response.text, "html.parser")
for link in soup.find_all('a'):
    print(link.get('href'))