# 函数定义
def greet(name, greeting="Hello"):
    """向用户打招呼（文档字符串）"""
    return f"{greeting}, {name}!"

print(greet("Alice"))              # Hello, Alice!
print(greet("Bob", "Hi"))          # Hi, Bob!
print(greet(greeting="Hey", name="Charlie"))  # Hey, Charlie!

# 查看文档
print(greet.__doc__)
help(greet)

# 位置参数
def describe_pet(name, animal_type="dog"):
    print(f"I have a {animal_type} named {name}")

describe_pet("Buddy")                    # 使用默认值
describe_pet("Whiskers", "cat")          # 位置参数
describe_pet(animal_type="fish", name="Nemo")  # 关键字参数

# 可变参数 *args
def sum_all(*args):
    """计算所有参数的和"""
    return sum(args)

print(sum_all(1, 2, 3))       # 6
print(sum_all(1, 2, 3, 4, 5)) # 15

# 关键字可变参数 **kwargs
def build_profile(**kwargs):
    """构建用户档案"""
    return kwargs

profile = build_profile(name="Alice", age=20, city="Beijing")
print(profile)  # {'name': 'Alice', 'age': 20, 'city': 'Beijing'}

# 混合使用
def func(a, b, *args, **kwargs):
    print(f"a={a}, b={b}")
    print(f"args={args}")
    print(f"kwargs={kwargs}")

func(1, 2, 3, 4, 5, x=10, y=20)

# 返回单个值
def square(x):
    return x ** 2

# 返回多个值（实际返回元组）
def min_max(numbers):
    return min(numbers), max(numbers)

lo, hi = min_max([3, 1, 4, 1, 5])
print(f"Min: {lo}, Max: {hi}")

# 没有return的函数返回None
def do_nothing():
    pass

result = do_nothing()
print(result)  # None

# 提前返回
def divide(a, b):
    if b == 0:
        return None  # 或者抛出异常
    return a / b

# 局部变量和全局变量
x = 10  # 全局变量

def outer():
    x = 20  # 外层函数的局部变量
    
    def inner():
        nonlocal x  # 引用外层函数的变量
        x = 30
        print(f"inner: x = {x}")
    
    inner()
    print(f"outer: x = {x}")

outer()
print(f"global: x = {x}")

# global关键字
count = 0

def increment():
    global count
    count += 1

increment()
increment()
print(count)  # 2

# 最佳实践：尽量避免使用global
def better_increment(current_count):
    return current_count + 1

count = better_increment(count)

# 基本lambda
square = lambda x: x ** 2
print(square(5))  # 25

# 多参数
add = lambda a, b: a + b
print(add(3, 5))  # 8

# 与高阶函数配合
numbers = [1, 2, 3, 4, 5]

# map
squared = list(map(lambda x: x**2, numbers))
print(squared)  # [1, 4, 9, 16, 25]

# filter
evens = list(filter(lambda x: x % 2 == 0, numbers))
print(evens)  # [2, 4]

# sorted
students = [("Alice", 90), ("Bob", 85), ("Charlie", 92)]
sorted_students = sorted(students, key=lambda s: s[1], reverse=True)
print(sorted_students)

# 立即调用的lambda
result = (lambda x, y: x + y)(3, 5)
print(result)  # 8

# 导入整个模块
import math
print(math.sqrt(16))  # 4.0
print(math.pi)        # 3.14159...

# 导入特定函数
from math import sqrt, pi
print(sqrt(16))

# 导入并重命名
from datetime import datetime as dt
now = dt.now()
print(now)

# 导入所有（不推荐）
# from math import *

# 自定义模块
# 假设 mymodule.py 中有：
# def add(a, b):
#     return a + b
# PI = 3.14159

# import mymodule
# print(mymodule.add(1, 2))
# print(mymodule.PI)

import time
import functools

def timer(func):
    """计时装饰器"""
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()
        print(f"{func.__name__} took {end - start:.4f}s")
        return result
    return wrapper

def memoize(func):
    """缓存装饰器"""
    cache = {}
    @functools.wraps(func)
    def wrapper(*args):
        if args not in cache:
            cache[args] = func(*args)
        return cache[args]
    return wrapper

@timer
@memoize
def fibonacci(n):
    if n < 2:
        return n
    return fibonacci(n - 1) + fibonacci(n - 2)

print(fibonacci(30))