如何使用python装饰器修复“ NoneType”错误？

Question

我正在使用带有装饰器的LRU（最近最少使用）缓存来存储最近使用的本地化，但是当我调用函数从.json文件中读取它时，出现“ NoneType”错误

def loc_cache(func):
    loc_cache.locale = {} # {lang:(local, count)} local:dict
    loc_cache.MAXLENGTH = 5
    def wrapper(key):
        print(key) #this function wasn't called
        if key not in loc_cache.locale.keys():
            try:
                locale = read_locale(key)
                loc_cache.locale[key] = (locale, 1)
                wrapper.locale = locale
            except KeyError:
                key = "en" # set default locale
                wrapper(key)
        else:
            locale, count = loc_cache.locale[key]
            loc_cache.locale[key] = (locale, count+1)
            wrapper.locale = locale
        return wrapper.locale

@loc_cache
def read_locale(key):
    locale = read_json("./config/locale.json", key)
    return locale

def auth(user:User):
    locale = read_locale(user.locale)
    print(locale["auth"])
    return

u = User(1) # __init__ takes 1 for id
u.locale = "en"
auth(u)

我希望它会返回存储在.json文件中的“ en”中的词组，但是它说

Traceback (most recent call last):
  File "main.py", line 61, in <module>
    auth(u)
  File "main.py", line 52, in auth
    locale = read_locale(user.locale)
TypeError: 'NoneType' object is not callable

Answer 1

您没有从装饰器返回包装函数，因此Python照常返回None ，并在您执行read_locale(user.locale)时尝试调用它。 你需要：

def loc_cache(func):
    loc_cache.locale = {} # {lang:(local, count)} local:dict
    loc_cache.MAXLENGTH = 5
    def wrapper(key):
        print(key) #this function wasn't called
        if key not in loc_cache.locale.keys():
            try:
                locale = read_locale(key)
                loc_cache.locale[key] = (locale, 1)
                wrapper.locale = locale
            except KeyError:
                key = "en" # set default locale
                wrapper(key)
        else:
            locale, count = loc_cache.locale[key]
            loc_cache.locale[key] = (locale, count+1)
            wrapper.locale = locale
        return wrapper.locale
    return wrapper
    # Here ^^^^

Answer 2

您没有在装饰器的末尾返回 wrapper器：

def loc_cache(func):
    loc_cache.locale = {} # {lang:(local, count)} local:dict
    loc_cache.MAXLENGTH = 5
    def wrapper(key):
        if key not in loc_cache.locale:
            try:
                locale = read_locale(key)
                loc_cache.locale[key] = (locale, 1)
            except KeyError:
                key = "en" # set default locale
                wrapper(key)
        else:
            locale, count = loc_cache.locale[key]
            loc_cache.locale[key] = (locale, count+1)
        wrapper.locale = locale
        return wrapper.locale
    return wrapper

装饰器通常将一个函数作为输入，然后返回一个函数。 在这里，您定义了一个内部函数，但是您忘了返回它。 结果，装饰器的输出为None ，并且您无法调用None 。