Flask - 'NoneType'对象不可调用

Question

我正在开发我的第一个Flask应用程序.直接服用一些代码出来这个,我想确保一个值是存在于用户的Cookie.

def after_this_request(f):
    if not hasattr(g, 'after_request_callbacks'):
        g.after_request_callbacks = []
    g.after_request_callbacks.append(f)
    return f

@app.after_request
def call_after_request_callbacks(response):
    for callback in getattr(g, 'after_request_callbacks', ()):
        response = callback(response)
    return response

@app.before_request
def detect_unique_id():
    unique_id = request.cookies.get('unique_id')
    if unique_id is None:
        unique_id = generate_unique_id()
        @after_this_request
        def remember_unique_id(response):
            response.set_cookie('unique_id', unique_id)
    g.unique_id = unique_id

我一直收到这个错误:

Traceback (most recent call last):
  File "/..../env/lib/python2.7/site-packages/flask/app.py", line 1701, in __call__
    return self.wsgi_app(environ, start_response)
  File "/..../env/lib/python2.7/site-packages/flask/app.py", line 1690, in wsgi_app
    return response(environ, start_response)
TypeError: 'NoneType' object is not callable

我试图了解这个错误的原因.请帮忙.

Answer 1

问题

remember_unique_id不会返回响应对象,而是call_after_request_callbacks将调用每个回调的结果分配给after_this_request装饰器result,然后返回它.也就是说:

# This
for callback in getattr(g, 'after_request_callbacks', ()):
    response = callback(response)

# translates to this
for callback in [remember_unique_id]:
    response = callback(response)

# which translates to this
response = remember_unique_id(response)

# which translates to this
response = None

解决方案

或者:

• 更新remember_unique_id以返回已修改的响应对象

• 更新call_after_request_callbacks以检查返回的对象并确保它不是None:

  for callback in getattr(g, 'after_request_callbacks', ()):
      result = callback(response)
      if result is not None:
          response = result
  

为什么会这样？

Flask是一个WSGI应用程序,它希望response是一个WSGI应用程序(即一个可调用的对象).当它处理来自视图模板的响应时,它会运行一些检查以确保它可以用作响应对象,如果返回的值不是WSGI应用程序,则将其转换为一个.它并没有检查响应对象并没有被改变的after_request装饰,所以当它试图调用响应对象(它假定在这一点上有效的WSGI应用程序),你得到的TypeError.