Python 完全指南

# todo_v1.py - 最基础的任务管理器 # === 1. 变量与数据类型 === # 使用列表存储任务 todos = [] # 空列表 todo_id = 1 # 任务ID计数器 # === 2. 函数定义 === def add_task(title, description=""): """添加新任务""" global todo_id # 字典存储任务信息 task = { "id": todo_id, "title": title, "description": description, "completed": False } todos.append(task) todo_id += 1 # f-string 格式化输出 print(f"✅ 任务 '{title}' 已添加！") return task def list_tasks(): """列出所有任务""" if not todos: # 判断列表是否为空 print("📋 暂无任务") return print(f"\n📋 共有 {len(todos)} 个任务:\n") # for循环遍历 for task in todos: status = "✅" if task["completed"] else "⭕" print(f"{status} [{task['id']}] {task['title']}") # 如果有描述，显示描述 if task["description"]: print(f" 💬 {task['description']}") def complete_task(task_id): """标记任务为完成""" # 使用enumerate获取索引和值 for i, task in enumerate(todos): if task["id"] == task_id: todos[i]["completed"] = True print(f"✅ 任务 '{task['title']}' 已完成！") return # 未找到任务 print(f"❌ 未找到ID为 {task_id} 的任务") def delete_task(task_id): """删除任务""" for i, task in enumerate(todos): if task["id"] == task_id: deleted = todos.pop(i) # pop删除并返回 print(f"🗑️ 任务 '{deleted['title']}' 已删除！") return print(f"❌ 未找到ID为 {task_id} 的任务") # === 3. 主程序循环 === def main(): """主函数""" print("🎯 TodoMaster v1.0") print("=" * 30) # while 无限循环 while True: print("\n命令: [a]添加 [l]列表 [c]完成 [d]删除 [q]退出") cmd = input("请输入命令: ").strip().lower() # if/elif/else 条件判断 if cmd == 'a': title = input("任务标题: ") desc = input("任务描述（可选）: ") add_task(title, desc) elif cmd == 'l': list_tasks() elif cmd == 'c': try: task_id = int(input("任务ID: ")) complete_task(task_id) except ValueError: print("❌ 请输入有效的数字ID") elif cmd == 'd': try: task_id = int(input("任务ID: ")) delete_task(task_id) except ValueError: print("❌ 请输入有效的数字ID") elif cmd == 'q': print("👋 再见！") break # 跳出循环 else: print("❌ 无效命令") # === 4. 程序入口 === if __name__ == "__main__": main()

# todo_v2.py - 面向对象版本 from datetime import datetime from typing import List, Optional # === 1. 定义Task类 === class Task: """任务类 - 封装任务的属性和行为""" # 类变量（所有实例共享） _id_counter = 1 def __init__(self, title: str, description: str = ""): """构造函数""" self.id = Task._id_counter Task._id_counter += 1 self.title = title self.description = description self.completed = False self.created_at = datetime.now() self.completed_at: Optional[datetime] = None def complete(self): """标记任务为完成""" self.completed = True self.completed_at = datetime.now() def to_dict(self) -> dict: """转换为字典""" return { "id": self.id, "title": self.title, "description": self.description, "completed": self.completed, "created_at": self.created_at.isoformat(), "completed_at": self.completed_at.isoformat() if self.completed_at else None } def __str__(self) -> str: """字符串表示（用于打印）""" status = "✅" if self.completed else "⭕" return f"{status} [{self.id}] {self.title}" def __repr__(self) -> str: """详细表示（用于调试）""" return f"Task(id={self.id}, title='{self.title}', completed={self.completed})" @staticmethod def from_dict(data: dict) -> 'Task': """从字典创建Task实例（用于反序列化）""" task = Task(data['title'], data.get('description', '')) task.id = data['id'] task.completed = data['completed'] return task # === 2. 定义TodoManager类 === class TodoManager: """任务管理器类 - 管理所有任务""" def __init__(self): self._tasks: List[Task] = [] # 私有属性（约定） def add_task(self, title: str, description: str = "") -> Task: """添加任务""" task = Task(title, description) self._tasks.append(task) print(f"✅ 任务 '{title}' 已添加！") return task def get_task(self, task_id: int) -> Optional[Task]: """根据ID获取任务""" for task in self._tasks: if task.id == task_id: return task return None def list_tasks(self, show_completed: bool = True): """列出任务""" tasks = self._tasks if show_completed else [ t for t in self._tasks if not t.completed ] if not tasks: print("📋 暂无任务") return print(f"\n📋 共有 {len(tasks)} 个任务:\n") for task in tasks: print(task) # 调用__str__ if task.description: print(f" 💬 {task.description}") def complete_task(self, task_id: int) -> bool: """完成任务""" task = self.get_task(task_id) if task: task.complete() print(f"✅ 任务 '{task.title}' 已完成！") return True print(f"❌ 未找到ID为 {task_id} 的任务") return False def delete_task(self, task_id: int) -> bool: """删除任务""" task = self.get_task(task_id) if task: self._tasks.remove(task) print(f"🗑️ 任务 '{task.title}' 已删除！") return True print(f"❌ 未找到ID为 {task_id} 的任务") return False @property # 属性装饰器 def total_tasks(self) -> int: """总任务数""" return len(self._tasks) @property def completed_tasks(self) -> int: """已完成任务数""" return sum(1 for t in self._tasks if t.completed) def __len__(self) -> int: """支持len()函数""" return self.total_tasks def __iter__(self): """支持迭代""" return iter(self._tasks) # === 3. 使用示例 === if __name__ == "__main__": manager = TodoManager() # 添加任务 manager.add_task("学习Python面向对象", "理解类、对象、封装") manager.add_task("完成项目") # 列出任务 manager.list_tasks() # 使用property print(f"\n📊 统计: {manager.completed_tasks}/{manager.total_tasks} 已完成") # 完成任务 manager.complete_task(1) # 支持len() print(f"总任务数: {len(manager)}") # 支持迭代 print("\n遍历所有任务:") for task in manager: print(f" - {task.title}")

# todo_v3.py - 添加文件存储和高级特性 import json from pathlib import Path from typing import Generator, Callable from functools import wraps import time # === 1. 装饰器 - 记录函数执行时间 === def timer(func: Callable) -> Callable: """装饰器：测量函数执行时间""" @wraps(func) # 保留原函数元数据 def wrapper(*args, **kwargs): start = time.time() result = func(*args, **kwargs) elapsed = time.time() - start print(f"⏱️ {func.__name__} 耗时: {elapsed:.3f}s") return result return wrapper # === 2. 上下文管理器 - 自动保存数据 === class TodoManager: def __init__(self, filename: str = "todos.json"): self.filename = Path(filename) self._tasks: List[Task] = [] self.load_from_file() # 使用上下文管理器自动保存 def __enter__(self): """进入with块""" return self def __exit__(self, exc_type, exc_val, exc_tb): """退出with块，自动保存""" self.save_to_file() return False # 不抑制异常 # === 3. 文件IO === def save_to_file(self): """保存到JSON文件""" data = [task.to_dict() for task in self._tasks] # with语句自动关闭文件 with open(self.filename, 'w', encoding='utf-8') as f: json.dump(data, f, ensure_ascii=False, indent=2) print(f"💾 数据已保存到 {self.filename}") @timer # 使用装饰器 def load_from_file(self): """从JSON文件加载""" if not self.filename.exists(): return try: with open(self.filename, 'r', encoding='utf-8') as f: data = json.load(f) self._tasks = [Task.from_dict(item) for item in data] print(f"📂 已从 {self.filename} 加载 {len(self._tasks)} 个任务") except json.JSONDecodeError as e: print(f"❌ 文件格式错误: {e}") # === 4. 生成器 - 按条件迭代任务 === def filter_tasks( self, predicate: Callable[[Task], bool] ) -> Generator[Task, None, None]: """生成器：按条件筛选任务""" for task in self._tasks: if predicate(task): yield task # yield使这成为生成器 def pending_tasks(self) -> Generator[Task, None, None]: """生成器：返回未完成的任务""" return self.filter_tasks(lambda t: not t.completed) # === 5. 使用示例 === if __name__ == "__main__": # 使用上下文管理器，自动保存 with TodoManager() as manager: manager.add_task("学习装饰器") manager.add_task("掌握生成器") manager.add_task("理解上下文管理器") # 使用生成器遍历（惰性求值，节省内存） print("\n未完成的任务:") for task in manager.pending_tasks(): print(f" - {task.title}") # 退出with块时自动调用save_to_file() print("\n✅ 程序结束，数据已自动保存")

# === 推导式 - Python的语法糖 === # 1. 列表推导式（List Comprehension） # 基础用法 squares = [x**2 for x in range(10)] # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] # 带条件过滤 evens = [x for x in range(20) if x % 2 == 0] # [0, 2, 4, 6, 8, 10, 12, 14, 16, 18] # 嵌套推导式 matrix = [[i*j for j in range(3)] for i in range(3)] # [[0, 0, 0], [0, 1, 2], [0, 2, 4]] # 2. 字典推导式（Dict Comprehension） # 基础用法 squares_dict = {x: x**2 for x in range(5)} # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16} # 字典反转 original = {'a': 1, 'b': 2, 'c': 3} reversed_dict = {v: k for k, v in original.items()} # {1: 'a', 2: 'b', 3: 'c'} # 带条件 filtered = {k: v for k, v in original.items() if v > 1} # {'b': 2, 'c': 3} # 3. 集合推导式（Set Comprehension） # 去重 unique_chars = {c.lower() for c in "Hello World"} # {'h', 'e', 'l', 'o', ' ', 'w', 'r', 'd'} # 数学集合 multiples = {x for x in range(20) if x % 3 == 0} # {0, 3, 6, 9, 12, 15, 18} # 4. 生成器表达式（Generator Expression） # 惰性求值，节省内存 gen = (x**2 for x in range(1000000)) # 不会立即计算 # 用于sum等函数 total = sum(x**2 for x in range(10)) # 285 # 5. 实际应用示例 # 处理文件数据 lines = [" hello ", " world ", " python "] cleaned = [line.strip().upper() for line in lines] # ['HELLO', 'WORLD', 'PYTHON'] # 提取数据 users = [ {'name': 'Alice', 'age': 25}, {'name': 'Bob', 'age': 17}, {'name': 'Charlie', 'age': 30} ] adults = [u['name'] for u in users if u['age'] >= 18] # ['Alice', 'Charlie']