Python 备忘清单，一眼扫完核心知识点

int_num = 42  # 整数
float_num = 3.14  # 浮点数
string_var = "Hello, Python!"  # 字符串
bool_var = True  # 布尔值

x = 10  # 变量赋值
y = "Python"

my_list = [1, 2, 3, "Python"]  # 列表
my_tuple = (1, 2, 3, "Tuple")  # 元组

my_dict = {'name': 'John', 'age': 25, 'city': 'Pythonville'}  # 字典

if x > 0:
    print("Positive")
elif x == 0:
    print("Zero")
else:
    print("Negative")
for item in my_list:
    print(item)
while condition:
    # code

def greet(name="User"): 
    return f"Hello, {name}!"
result = greet("John")

class Dog:
    def __init__(self, name): 
        self.name = name
    def bark(self): 
        print("Woof!")

my_dog = Dog("Buddy")
my_dog.bark()

with open("file.txt", "r") as file: 
    content = file.read()

with open("new_file.txt", "w") as new_file: 
    new_file.write("Hello, Python!")

try: 
    result = 10 / 0 
except ZeroDivisionError: 
    print("Cannot divide by zero!")
finally: 
    print("Execution completed.")

import math
from datetime import datetime 
result = math.sqrt(25) 
current_time = datetime.now()

squares = [x**2 for x in range(5)]  # 列表推导式

add = lambda x, y: x + y 
result = add(2, 3)

# 创建虚拟环境
python -m venv myenv

# 激活虚拟环境
source myenv/bin/activate  # 在Unix或MacOS
myenv\Scripts\activate  # 在Windows

# 停用虚拟环境
deactivate

# 安装包
pip install package_name

# 列出已安装的包
pip list

# 创建requirements.txt
pip freeze > requirements.txt

# 从requirements.txt安装包
pip install -r requirements.txt

import json
# 将Python对象转换为JSON
json_data = json.dumps({"name": "John", "age": 25})

# 将JSON转换为Python对象
python_obj = json.loads(json_data)

import re
pattern = r'\d+'  # 匹配一个或多个数字
result = re.findall(pattern, "There are 42 apples and 123 oranges.")

from datetime import datetime, timedelta
current_date = datetime.now()
future_date = current_date + timedelta(days=7)

numbers = [1, 2, 3, 4, 5]
# 过滤
evens = list(filter(lambda x: x % 2 == 0, numbers))

# 映射
squared = list(map(lambda x: x**2, numbers))

# 归约 (需要functools)
from functools import reduce
product = reduce(lambda x, y: x * y, numbers)

my_dict = {'a': 1, 'b': 2, 'c': 3}
# 获取值
value = my_dict.get('d', 0)

# 字典推导式
squared_dict = {key: value**2 for key, value in my_dict.items()}

import threading
def print_numbers(): 
    for i in range(5): 
        print(i)
thread = threading.Thread(target=print_numbers)
thread.start()

import asyncio
async def print_numbers(): 
    for i in range(5): 
        print(i)
        await asyncio.sleep(1)
asyncio.run(print_numbers())

from bs4 import BeautifulSoup
import requests
url = "https://example.com"
response = requests.get(url)
soup = BeautifulSoup(response.text, 'html.parser')
title = soup.title.text

from flask import Flask, jsonify, request
app = Flask(__name__)

@app.route('/api/data', methods=['GET'])
def get_data():
    data = {'key': 'value'}
    return jsonify(data)

if __name__ == '__main__':
    app.run(debug=True)

import unittest

def add(x, y): 
    return x + y

class TestAddition(unittest.TestCase):
    def test_add_positive_numbers(self): 
        self.assertEqual(add(2, 3), 5)

if __name__ == '__main__':
    unittest.main()

import sqlite3
conn = sqlite3.connect('example.db')
cursor = conn.cursor()
# 执行SQL查询
cursor.execute('CREATE TABLE IF NOT EXISTS users (id INTEGER PRIMARY KEY, name')
# 提交更改
conn.commit()
# 关闭连接
conn.close()

# 写入文件
with open('example.txt', 'w') as file:
    file.write('Hello, Python!')

# 读取文件
with open('example.txt', 'r') as file:
    content = file.read()

try: 
    result = 10 / 0 
except ZeroDivisionError as e: 
    print(f"Error: {e}")
except Exception as e: 
    print(f"Unexpected Error: {e}")
else: 
    print("No errors occurred.")
finally: 
    print("This block always executes.")

def decorator(func): 
    def wrapper(): 
        print("Before function execution")
        func() 
        print("After function execution")
    return wrapper 

@decorator 
def my_function(): 
    print("Inside the function")

my_function()

from enum import Enum

class Color(Enum): 
    RED = 1 
    GREEN = 2 
    BLUE = 3
print(Color.RED)

set1 = {1, 2, 3}
set2 = {3, 4, 5}
# 并集
union_set = set1 | set2
# 交集
intersection_set = set1 & set2
# 差集
difference_set = set1 - set2

numbers = [1, 2, 3, 4, 5]
# 偶数的平方
squares = [x**2 for x in numbers if x % 2 == 0]

add = lambda x, y: x + y
result = add(3, 5)

from concurrent.futures import ThreadPoolExecutor

def square(x): 
    return x**2

with ThreadPoolExecutor() as executor: 
    results = executor.map(square, [1, 2, 3, 4, 5])

import gettext

# 设置语言
lang = 'en_US'
_ = gettext.translation('messages', localedir='locale', languages=[lang]).gette
print(_("Hello, World!"))

# 创建虚拟环境
python -m venv myenv

# 激活虚拟环境
source myenv/bin/activate  # 在Unix/Linux
myenv\Scripts\activate  # 在Windows

# 停用虚拟环境
deactivate

from datetime import datetime, timedelta

now = datetime.now()
# 格式化日期
formatted_date = now.strftime('%Y-%m-%d %H:%M:%S')
# 给日期添加天数
future_date = now + timedelta(days=7)

my_dict = {'name': 'John', 'age': 30}
# 获取值，并设置默认值
age = my_dict.get('age', 25)
# 遍历键和值
for key, value in my_dict.items():
    print(f"{key}: {value}")

import re
text = "Hello, 123 World!"
# 匹配数字
numbers = re.findall(r'\d+', text)

def square_numbers(n): 
    for i in range(n): 
        yield i**2

squares = square_numbers(5)

import sqlite3
# 连接SQLite数据库
conn = sqlite3.connect('mydatabase.db')
cursor = conn.cursor()
# 执行SQL查询
cursor.execute('SELECT * FROM mytable')

import zipfile

with zipfile.ZipFile('archive.zip', 'w') as myzip:
    myzip.write('file.txt')

with zipfile.ZipFile('archive.zip', 'r') as myzip:
    myzip.extractall('extracted')

import requests
from bs4 import BeautifulSoup

url = 'https://example.com'
response = requests.get(url)
soup = BeautifulSoup(response.text, 'html.parser')
# 从HTML提取数据
title = soup.title.text

import smtplib
from email.mime.text import MIMEText

# 设置邮件服务器
server = smtplib.SMTP('smtp.gmail.com', 587)
server.starttls()

# 登录邮箱账户
server.login('your_email@gmail.com', 'your_password')

# 发送邮件
msg = MIMEText('Hello, Python!')
msg['Subject'] = 'Python Email'
server.sendmail('your_email@gmail.com', 'recipient@example.com', msg.as_string())

import json
data = {'name': 'John', 'age': 30}

# 写入JSON文件
with open('data.json', 'w') as json_file:
    json.dump(data, json_file)

# 从JSON文件读取
with open('data.json', 'r') as json_file:
    loaded_data = json.load(json_file)