python - Flask:如果字段不存在，则 current_app AttributeError

Question

我尝试为 Flask 创建两个装饰器来装饰一个简单的函数。两个装饰器都需要访问 current_app 上的相同字段/属性。装饰函数也需要访问相同的属性。但我想测试这个字段是否已经存在并在任一装饰器中获取它的值。如果它已经存在，则测试是否存在确实有效，但如果它尚不存在，则返回 AttributeError。例如:如果字段不存在，测试“None”或使用 hasattr/getattr 会给出 AttributeError。

例如:

if current_app.exists is None:

给予:

AttributeError: 'Flask' object has no attribute 'exists'

try/catch 是处理这个问题的正确方法吗？

def first(org_func):
    @wraps(org_func)
    def decorated_function(*args, **kwargs):
        try:
            current_app.exists = current_app.exists + ' and then first'
        except AttributeError:
            current_app.exists = 'first'
        print(current_app.exists)
        return org_func(*args, **kwargs)
    return decorated_function

def second(org_func):
    @wraps(org_func)
    def decorated_function(*args, **kwargs):
        try:
            current_app.exists = current_app.exists + ' and then second'
        except AttributeError:
            current_app.exists = 'second'
        print(current_app.exists)
        return org_func(*args, **kwargs)
    return decorated_function

@first    
@second  
def get(self):
    print('original function calling ' + current_app.exists)
    return {'message': 'ok'}

Answer 1

您可以使用内置函数 hasattr 来实现此目的。它本质上与你的装饰器做同样的事情

hasattr(obj, name, /)
    Return whether the object has an attribute with the given name.

    This is done by calling getattr(obj, name) and catching AttributeError.

例如:

if hasattr(current_app, 'exists'):
    print("current_app has 'exists' attribute")
else:
    print("current_app does not have 'exists' attribute")

或者，您可以使用带有默认值的 getattr，例如:

exists_first = getattr(current_app, 'exists', 'first')
# if current_app has an 'exists' attribute, then exists_first == current_app.exists
# if current_app does NOT have an 'exists' attribue, then exists_first == 'first'
exists_second = getattr(current_app, 'exists', 'second')
# if current_app has an 'exists' attribute, then exists_second == current_app.exists
# if current_app does NOT have an 'exists' attribue, then exists_second == 'second'