# 整数
age = 25

# 浮点数
height = 1.75

# 字符串
name = "Alice"
message = 'Hello, Python!'

# 布尔值
is_student = True
is_empty = False

# 空值
result = None

# 查看数据类型
print(type(age))        # <class 'int'>
print(type(height))     # <class 'float'>
print(type(name))       # <class 'str'>

# 创建列表
fruits = ["apple", "banana", "orange"]
numbers = list(range(1, 6))  # [1, 2, 3, 4, 5]

# 添加元素
fruits.append("grape")       # 末尾添加
fruits.insert(0, "mango")    # 指定位置插入

# 删除元素
fruits.remove("banana")      # 按值删除
popped = fruits.pop()        # 弹出末尾元素

# 切片
print(fruits[0])             # 第一个元素
print(fruits[-1])            # 最后一个元素
print(fruits[1:3])           # 切片：索引1到2
print(fruits[::2])           # 步长2

# 列表推导式
squares = [x**2 for x in range(10)]
evens = [x for x in range(20) if x % 2 == 0]

# 创建元组
point = (3, 4)
colors = ("red", "green", "blue")

# 单元素元组（必须加逗号）
single = (42,)  

# 解包
x, y = point
a, b, c = colors

# 常用方法
print(colors.index("red"))   # 0
print(colors.count("blue")) # 1

# 创建集合
skills = {"Python", "Java", "Go", "Python"}
print(skills)  # {'Python', 'Java', 'Go'}  自动去重

# 集合运算
set1 = {1, 2, 3, 4}
set2 = {3, 4, 5, 6}
print(set1 & set2)  # {3, 4} 交集
print(set1 | set2)  # {1, 2, 3, 4, 5, 6} 并集
print(set1 - set2)  # {1, 2} 差集
print(set1 ^ set2)  # {1, 2, 5, 6} 对称差集

# 添加 / 删除
skills.add("Rust")
skills.discard("Java")   # 安全删除，不存在不报错
skills.remove("Go")      # 删除，不存在抛异常

# 创建字典
person = {
    "name": "Alice",
    "age": 25,
    "city": "Shanghai"
}

# 访问
print(person["name"])          # Alice
print(person.get("age", 0))    # 25，默认值

# 添加 / 修改
person["email"] = "alice@example.com"
person["age"] = 26

# 删除
del person["city"]
popped = person.pop("email")

# 遍历
for key, value in person.items():
    print(f"{key}: {value}")

for key in person.keys():
    print(key)

for value in person.values():
    print(value)

# 字典推导式
squares_dict = {x: x**2 for x in range(5)}

score = 85

if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 60:
    grade = "C"
else:
    grade = "D"

print(f"成绩等级: {grade}")

# 三元表达式
result = "及格" if score >= 60 else "不及格"

# 基本语法
for i in range(5):
    print(i)  # 0 1 2 3 4

# 遍历列表
animals = ["cat", "dog", "bird"]
for animal in animals:
    print(animal)

# 带索引
for index, animal in enumerate(animals):
    print(f"{index}: {animal}")

# 遍历字典
user = {"name": "Bob", "age": 30}
for key, value in user.items():
    print(f"{key} = {value}")

count = 0
while count < 5:
    print(count)
    count += 1
else:
    print("循环正常结束")  # else 在循环正常结束时执行

# 无限循环 + break
while True:
    response = input("输入 'quit' 退出: ")
    if response == "quit":
        break
    print(f"你输入了: {response}")

# break: 跳出当前循环
for i in range(10):
    if i == 5:
        break
    print(i)  # 0 1 2 3 4

# continue: 跳过当前迭代
for i in range(5):
    if i == 2:
        continue
    print(i)  # 0 1 3 4

# pass: 占位符，不做任何操作
for i in range(5):
    if i == 2:
        pass  # TODO: 稍后实现
    else:
        print(i)

# 基本函数
def greet(name):
    """问候函数，返回问候语"""
    return f"Hello, {name}!"

message = greet("Alice")
print(message)  # Hello, Alice!

# 默认参数
def power(base, exponent=2):
    return base ** exponent

print(power(3))      # 9，使用默认值
print(power(2, 3))  # 8，显式指定

# 可变参数 *args
def sum_all(*numbers):
    total = 0
    for n in numbers:
        total += n
    return total

print(sum_all(1, 2, 3, 4, 5))  # 15

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

print_info(name="Bob", age=30, city="Beijing")

# 无返回值（默认返回 None）
def print_hello():
    print("Hello!")

# 单返回值
def square(x):
    return x * x

# 多返回值（返回元组）
def divide(a, b):
    quotient = a // b
    remainder = a % b
    return quotient, remainder

q, r = divide(10, 3)
print(f"商={q}, 余数={r}")  # 商=3, 余数=1

# lambda: 匿名函数，适合简短函数
square = lambda x: x ** 2
print(square(5))  # 25

# 配合内置函数使用
numbers = [1, 2, 3, 4, 5]
filtered = list(filter(lambda x: x % 2 == 0, numbers))
print(filtered)  # [2, 4]

mapped = list(map(lambda x: x * 2, numbers))
print(mapped)  # [2, 4, 6, 8, 10]

sorted_list = sorted(numbers, key=lambda x: -x)  # 降序排列
print(sorted_list)  # [5, 4, 3, 2, 1]

import time

def timer(func):
    """计时装饰器"""
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()
        print(f"{func.__name__} 执行耗时: {end - start:.4f}秒")
        return result
    return wrapper

@timer
def slow_function():
    time.sleep(1)
    return "Done"

print(slow_function())
# slow_function 执行耗时: 1.0012秒
# Done

class Dog:
    """狗类"""
    
    # 类属性（所有实例共享）
    species = "犬科"
    
    def __init__(self, name, age):
        """初始化方法"""
        self.name = name    # 实例属性
        self.age = age
    
    def bark(self):
        """叫声方法"""
        return f"{self.name} 汪汪叫！"
    
    def get_info(self):
        return f"{self.name}, {self.age}岁"
    
    def __str__(self):
        """字符串表示"""
        return f"Dog({self.name})"

# 创建实例
dog1 = Dog("旺财", 3)
dog2 = Dog("小白", 1)

print(dog1.bark())           # 旺财 汪汪叫！
print(dog2.get_info())       # 小白, 1岁
print(Dog.species)           # 犬科
print(dog1)                  # Dog(旺财)

class Animal:
    def __init__(self, name):
        self.name = name
    
    def speak(self):
        raise NotImplementedError("子类必须实现此方法")

class Cat(Animal):
    def speak(self):
        return f"{self.name} 喵~"

class Dog(Animal):
    def speak(self):
        return f"{self.name} 汪！"

# 多态：同一接口，不同实现
animals = [Cat("咪咪"), Dog("旺财")]
for animal in animals:
    print(animal.speak())
# 咪咪 喵~
# 旺财 汪！

class User:
    def __init__(self, username, password):
        self.username = username        # 公有属性
        self.__password = password      # 私有属性（名称重整）
    
    def check_password(self, pwd):
        return self.__password == pwd
    
    @property
    def password(self):
        """属性访问器，只读"""
        return "******"

user = User("alice", "secret123")
print(user.username)          # alice
print(user.password)          # ******
print(user.check_password("secret123"))  # True

# print(user.__password)     # AttributeError: 访问不到！

# 导入整个模块
import math
print(math.pi)           # 3.141592653589793
print(math.sqrt(16))     # 4.0

# 导入特定成员
from random import randint, choice
print(randint(1, 10))    # 1~10 随机整数
print(choice(["a", "b", "c"]))  # 随机选一个

# 导入并起别名
import datetime as dt
now = dt.datetime.now()
print(now)               # 2026-05-27 11:45:00.xxx

# 导入所有（不推荐）
from math import *

# 实战示例：os 和 pathlib
import os
from pathlib import Path

# 当前目录
cwd = Path.cwd()
print(cwd)

# 遍历目录
for item in cwd.iterdir():
    print(item.name)

# 路径拼接
file_path = cwd / "data" / "example.txt"
print(file_path.exists())

# collections 计数器
from collections import Counter
words = ["apple", "banana", "apple", "cherry", "banana", "apple"]
counter = Counter(words)
print(counter.most_common(2))  # [("apple", 3), ("banana", 2)]

# __init__.py 中可以指定默认导出
# from .module1 import Something

# 使用包
# from mypackage import module1
# module1.do_something()

try:
    num = int(input("输入一个整数: "))
    result = 10 / num
    print(f"10 / {num} = {result}")
except ValueError:
    print("输入无效，请输入整数！")
except ZeroDivisionError:
    print("除数不能为零！")
except Exception as e:
    print(f"未知错误: {e}")
else:
    print("全部执行成功，没有异常")
finally:
    print("无论是否出错，都会执行")

def divide(a, b):
    if b == 0:
        raise ZeroDivisionError("除数不能为0")
    return a / b

try:
    result = divide(10, 0)
except ZeroDivisionError as e:
    print(e)  # 除数不能为0

class ValidationError(Exception):
    """自定义验证异常"""
    def __init__(self, field, message):
        self.field = field
        self.message = message
        super().__init__(f"{field}: {message}")

def validate_age(age):
    if age < 0:
        raise ValidationError("age", "年龄不能为负数")
    if age > 150:
        raise ValidationError("age", "年龄不合理")
    return True

try:
    validate_age(-5)
except ValidationError as e:
    print(e)  # age: 年龄不能为负数

# 读取文件
with open("example.txt", "r", encoding="utf-8") as f:
    content = f.read()          # 读取全部
    # content = f.readline()   # 读取一行
    # content = f.readlines()  # 读取所有行到列表

# 写入文件
with open("output.txt", "w", encoding="utf-8") as f:
    f.write("第一行内容\n")
    f.write("第二行内容\n")

# 追加模式
with open("log.txt", "a", encoding="utf-8") as f:
    f.write("新的日志记录\n")

import json

# 写入 JSON
data = {
    "name": "Alice",
    "age": 25,
    "skills": ["Python", "Java", "Go"]
}

with open("user.json", "w", encoding="utf-8") as f:
    json.dump(data, f, ensure_ascii=False, indent=2)

# 读取 JSON
with open("user.json", "r", encoding="utf-8") as f:
    loaded = json.load(f)
    print(loaded["name"])  # Alice