def create_counter(initial=0):
    """創(chuàng)建一個(gè)簡單的計(jì)數(shù)器"""
    count = [initial]  # 使用列表來包裝計(jì)數(shù)器值
    
    def increment():
        count[0] += 1
        return count[0]
    
    return increment

# 函數(shù)定義時(shí)發(fā)生了什么？
print("函數(shù)定義時(shí): create_counter函數(shù)對(duì)象被創(chuàng)建")
print("默認(rèn)參數(shù)initial=0被計(jì)算并存儲(chǔ)")

def problematic_function(items=[]):
    """有問題的函數(shù)：使用可變默認(rèn)參數(shù)"""
    items.append(len(items))
    return items

# 查看函數(shù)的默認(rèn)參數(shù)存儲(chǔ)
print("函數(shù)的__defaults__屬性:", problematic_function.__defaults__)
print("默認(rèn)參數(shù)的id:", id(problematic_function.__defaults__[0]))

# 多次調(diào)用函數(shù)
result1 = problematic_function()
print("第一次調(diào)用結(jié)果:", result1, "id:", id(result1))

result2 = problematic_function()
print("第二次調(diào)用結(jié)果:", result2, "id:", id(result2))

result3 = problematic_function()
print("第三次調(diào)用結(jié)果:", result3, "id:", id(result3))

print("\n問題顯現(xiàn)：所有調(diào)用都返回同一個(gè)列表對(duì)象！")
print("result1 is result2:", result1 is result2)
print("result1 is result3:", result1 is result3)

import dis

def analyze_function(func):
    """分析函數(shù)的字節(jié)碼"""
    print(f"\n分析函數(shù): {func.__name__}")
    print("=" * 50)
    dis.dis(func)
    
    # 查看co_consts（常量池）
    print(f"\n函數(shù)常量池 (co_consts): {func.__code__.co_consts}")
    
    # 查看默認(rèn)參數(shù)值
    if func.__defaults__:
        print(f"默認(rèn)參數(shù)值 (__defaults__): {func.__defaults__}")
        for i, default in enumerate(func.__defaults__):
            print(f"  參數(shù){i}: {default} (id: {id(default)})")

# 分析有問題的函數(shù)
analyze_function(problematic_function)

# 對(duì)比：分析使用不可變默認(rèn)參數(shù)的函數(shù)
def safe_function(count=0):
    """安全的函數(shù)：使用不可變默認(rèn)參數(shù)"""
    count += 1
    return count

analyze_function(safe_function)

def get_cached_data(key, cache={}):
    """有問題的緩存實(shí)現(xiàn)：所有調(diào)用共享同一個(gè)cache字典"""
    if key in cache:
        print(f"緩存命中: {key}")
        return cache[key]
    
    # 模擬昂貴的計(jì)算
    print(f"計(jì)算: {key}")
    result = f"result_for_{key}"
    cache[key] = result
    return result

# 測試緩存函數(shù)
print("=== 測試有問題的緩存函數(shù) ===")
print("第一次調(diào)用 get_cached_data('a'):", get_cached_data('a'))
print("第二次調(diào)用 get_cached_data('a'):", get_cached_data('a'))
print("第三次調(diào)用 get_cached_data('b'):", get_cached_data('b'))

# 問題：不同的調(diào)用者會(huì)共享cache！
print("\n=== 模擬不同調(diào)用者 ===")
def caller1():
    return get_cached_data('x')

def caller2():
    return get_cached_data('x')

print("caller1調(diào)用結(jié)果:", caller1())
print("caller2調(diào)用結(jié)果（意外命中緩存）:", caller2())

# 查看緩存內(nèi)容
print("\n緩存內(nèi)容:", problematic_function.__defaults__[0] if problematic_function.__defaults__ else "無")

def create_user(name, permissions=[]):
    """創(chuàng)建用戶并分配權(quán)限"""
    user = {
        'name': name,
        'permissions': permissions
    }
    return user

print("=== 測試用戶創(chuàng)建函數(shù) ===")

# 創(chuàng)建多個(gè)用戶
user1 = create_user('Alice')
user1['permissions'].append('read')  # 只為Alice添加read權(quán)限

user2 = create_user('Bob')
user2['permissions'].append('write')  # 本意是為Bob添加write權(quán)限

user3 = create_user('Charlie')

print(f"user1: {user1}")
print(f"user2: {user2}")
print(f"user3: {user3}")

print("\n災(zāi)難：所有用戶的permissions都變成了['read', 'write']！")
print("user1['permissions'] is user2['permissions']:", 
      user1['permissions'] is user2['permissions'])

def create_matrix(rows=3, cols=3, default_value=0, matrix=None):
    """
    創(chuàng)建矩陣的復(fù)雜示例
    問題：多層嵌套的默認(rèn)參數(shù)
    """
    if matrix is None:
        matrix = []
    
    for i in range(rows):
        row = []
        for j in range(cols):
            row.append(default_value)
        matrix.append(row)
    
    return matrix

print("=== 測試矩陣創(chuàng)建函數(shù) ===")

# 第一次調(diào)用
matrix1 = create_matrix(2, 2, 1)
print("matrix1 (2x2, 默認(rèn)值1):", matrix1)

# 修改matrix1
matrix1[0][0] = 99
print("修改后 matrix1:", matrix1)

# 第二次調(diào)用，使用默認(rèn)參數(shù)
matrix2 = create_matrix(2, 2, 2)
print("matrix2 (2x2, 默認(rèn)值2):", matrix2)

print("\n意外：matrix2受到了matrix1修改的影響！")
print("原因：默認(rèn)參數(shù)matrix=[]在所有調(diào)用間共享")

def safe_function_with_list(items=None):
    """安全的函數(shù)：使用None作為默認(rèn)值"""
    if items is None:
        items = []  # 每次調(diào)用創(chuàng)建新的列表
    
    items.append(len(items))
    return items

print("=== 使用None作為默認(rèn)值 ===")

# 多次調(diào)用測試
results = []
for i in range(3):
    result = safe_function_with_list()
    results.append(result)
    print(f"調(diào)用{i+1}: {result} (id: {id(result)})")

# 驗(yàn)證每個(gè)結(jié)果都是不同的對(duì)象
print("\n所有結(jié)果都是不同的對(duì)象:")
for i in range(len(results)):
    for j in range(i+1, len(results)):
        print(f"  result{i} is result{j}: {results[i] is results[j]}")

# 測試傳入自定義列表的情況
custom_list = [10, 20]
result = safe_function_with_list(custom_list)
print(f"\n傳入自定義列表: {result}")
print(f"原列表也被修改: {custom_list}")

# 創(chuàng)建一個(gè)唯一的哨兵對(duì)象
_SENTINEL = object()

def advanced_safe_function(items=_SENTINEL):
    """
    使用唯一哨兵對(duì)象作為默認(rèn)值
    優(yōu)點(diǎn)：允許None作為合法參數(shù)值
    """
    if items is _SENTINEL:
        items = []
    
    items.append(len(items))
    return items

print("=== 使用唯一哨兵對(duì)象 ===")

# 測試None作為參數(shù)
print("傳入None:", advanced_safe_function(None))
print("使用默認(rèn)值:", advanced_safe_function())
print("傳入空列表:", advanced_safe_function([]))

# 驗(yàn)證哨兵對(duì)象的唯一性
print(f"\n哨兵對(duì)象id: {id(_SENTINEL)}")
print(f"是否唯一: {_SENTINEL is object()}")

from functools import wraps
import inspect

def sanitize_defaults(func):
    """
    裝飾器：自動(dòng)處理可變默認(rèn)參數(shù)
    將可變默認(rèn)參數(shù)替換為None
    """
    # 獲取函數(shù)簽名
    sig = inspect.signature(func)
    
    @wraps(func)
    def wrapper(*args, **kwargs):
        # 綁定參數(shù)
        bound_args = sig.bind(*args, **kwargs)
        bound_args.apply_defaults()
        
        # 檢查并處理可變默認(rèn)參數(shù)
        for param_name, param in sig.parameters.items():
            if param_name in bound_args.arguments:
                default =