Python 入门手册——从安装到 Web 开发

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Python 入门手册——从安装到 Web 开发

作者： CaoZH
日期： 2024-06-15
本文为原创教程

Python 连续多年在 TIOBE 指数排名前三，在 AI、数据处理、Web 开发、自动化运维等领域都有广泛应用。2024 年，Python 3.12 已经是稳定版本。

本文从零开始，带你入门 Python 编程并搭建一个简单的 Web 应用。

一、安装 Python

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# Ubuntu/Debian
sudo apt update
sudo apt install -y python3 python3-pip python3-venv

# macOS
brew install python@3.12

# Windows
# 从 https://python.org 下载安装包

# 验证安装
python3 --version        # Python 3.12.x
pip3 --version

二、基础语法速览

变量与类型

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# 动态类型，不需要声明类型
name = "张三"            # str
age = 28                 # int
height = 1.75            # float
is_student = False       # bool
hobbies = ["读书", "跑步", "编码"]  # list
person = {"name": "李四", "age": 30}  # dict

# 类型转换
str(123)        # "123"
int("456")      # 456
float("3.14")   # 3.14

# 字符串操作
name = "Python"
print(name[0])        # P
print(name[-1])       # n
print(name[1:3])      # yt
print(f"Hello {name}!")  # f-string，最推荐的格式化方式

流程控制

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# if-elif-else
score = 85
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
else:
    grade = "D"

# for 循环
for i in range(5):
    print(i)        # 0 1 2 3 4

for idx, item in enumerate(hobbies):
    print(f"{idx}: {item}")

# while 循环
count = 0
while count < 3:
    print(count)
    count += 1

# 列表推导式（Python 特色）
squares = [x**2 for x in range(10)]    # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
evens = [x for x in range(20) if x % 2 == 0]

函数

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# 基本函数
def greet(name: str) -> str:
    """给用户打招呼"""
    return f"你好，{name}！"

# 默认参数
def create_user(name, age=18, city="未知"):
    return {"name": name, "age": age, "city": city}

# 可变参数
def sum_all(*args):
    return sum(args)

# 关键字参数
def print_info(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

# Lambda 匿名函数
numbers = [1, 2, 3, 4, 5]
doubled = list(map(lambda x: x * 2, numbers))  # [2, 4, 6, 8, 10]

三、文件与异常处理

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# 读取文件（推荐使用 with 语句）
with open("data.txt", "r", encoding="utf-8") as f:
    content = f.read()         # 全部读取
    lines = f.readlines()      # 按行读取

# 写入文件
with open("output.txt", "w", encoding="utf-8") as f:
    f.write("Hello, World!")

# 异常处理
try:
    result = 10 / 0
except ZeroDivisionError as e:
    print(f"除数不能为零: {e}")
except Exception as e:
    print(f"其他错误: {e}")
finally:
    print("无论如何都会执行")

四、实战：用 Flask 搭建 Web API

安装 Flask

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# 创建虚拟环境（强烈推荐）
mkdir my-web-app && cd my-web-app
python3 -m venv venv
source venv/bin/activate      # Linux/Mac
# venv\Scripts\activate       # Windows

# 安装依赖
pip install flask

创建应用

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# app.py
from flask import Flask, request, jsonify
from datetime import datetime

app = Flask(__name__)

# 模拟数据库
users = []
next_id = 1

# 首页
@app.route('/')
def home():
    return jsonify({
        "message": "Welcome to Python API",
        "version": "1.0.0",
        "endpoints": {
            "GET /users": "获取用户列表",
            "GET /users/<id>": "获取单个用户",
            "POST /users": "创建用户",
            "PUT /users/<id>": "更新用户",
            "DELETE /users/<id>": "删除用户"
        }
    })

# 获取用户列表
@app.route('/users', methods=['GET'])
def get_users():
    return jsonify({
        "code": 200,
        "data": users,
        "total": len(users)
    })

# 获取单个用户
@app.route('/users/<int:user_id>', methods=['GET'])
def get_user(user_id):
    user = next((u for u in users if u['id'] == user_id), None)
    if user is None:
        return jsonify({"code": 404, "message": "用户不存在"}), 404
    return jsonify({"code": 200, "data": user})

# 创建用户
@app.route('/users', methods=['POST'])
def create_user():
    global next_id
    data = request.get_json()

    if not data or not data.get('name'):
        return jsonify({"code": 400, "message": "缺少必要字段 name"}), 400

    user = {
        "id": next_id,
        "name": data['name'],
        "email": data.get('email', ''),
        "age": data.get('age', 0),
        "created_at": datetime.now().isoformat()
    }
    next_id += 1
    users.append(user)

    return jsonify({"code": 200, "message": "创建成功", "data": user}), 201

# 更新用户
@app.route('/users/<int:user_id>', methods=['PUT'])
def update_user(user_id):
    user = next((u for u in users if u['id'] == user_id), None)
    if user is None:
        return jsonify({"code": 404, "message": "用户不存在"}), 404

    data = request.get_json()
    user['name'] = data.get('name', user['name'])
    user['email'] = data.get('email', user['email'])
    user['age'] = data.get('age', user['age'])

    return jsonify({"code": 200, "message": "更新成功", "data": user})

# 删除用户
@app.route('/users/<int:user_id>', methods=['DELETE'])
def delete_user(user_id):
    global users
    user = next((u for u in users if u['id'] == user_id), None)
    if user is None:
        return jsonify({"code": 404, "message": "用户不存在"}), 404

    users = [u for u in users if u['id'] != user_id]
    return jsonify({"code": 200, "message": "删除成功"})

if __name__ == '__main__':
    app.run(debug=True, port=5000)

运行与测试

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# 启动
python app.py
# 输出：Running on http://127.0.0.1:5000

# 测试 API
curl http://localhost:5000/

curl -X POST http://localhost:5000/users \
  -H "Content-Type: application/json" \
  -d '{"name":"张三","email":"zhangsan@test.com","age":28}'

curl http://localhost:5000/users

curl -X PUT http://localhost:5000/users/1 \
  -H "Content-Type: application/json" \
  -d '{"age":29}'

curl -X DELETE http://localhost:5000/users/1

五、常用标准库

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# os — 操作系统接口
import os
os.getcwd()                     # 当前目录
os.listdir('.')                 # 列出文件
os.environ.get('HOME')          # 环境变量

# json — JSON 处理
import json
data = {"name": "Python", "version": 3.12}
json_str = json.dumps(data, ensure_ascii=False)
obj = json.loads(json_str)

# datetime — 日期时间
from datetime import datetime, timedelta
now = datetime.now()
yesterday = now - timedelta(days=1)
formatted = now.strftime("%Y-%m-%d %H:%M:%S")

# re — 正则表达式
import re
pattern = r'\d+'
result = re.findall(pattern, "abc123def456")  # ['123', '456']

六、包管理

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# pip 基本命令
pip install requests          # 安装包
pip install flask==3.0.0      # 指定版本
pip uninstall requests        # 卸载
pip list                      # 列出已安装
pip freeze > requirements.txt # 导出依赖
pip install -r requirements.txt # 安装依赖

七、总结

通过本教程，你学会了：

内容 掌握程度
✅ Python 基础语法 变量、类型、流程控制
✅ 函数与模块 函数定义、参数、标准库
✅ 文件与异常 文件读写、异常处理
✅ Flask Web 开发 RESTful API 构建
✅ 包管理 pip、虚拟环境

首发于 CaoZH 的笔记

CaoZHProgrammer

学习使我快乐。