python lines that start with @ [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

Understanding Python decorators

I was reading a django app source code where I find this

@login_required
def activities(request = None,\
            project_id = 0,\
          开发者_Go百科  task_id = 0,\
            ...

What does the line that start with @ mean?

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It's a decorator. What it does is basically wrap the function. It is equivalent with this code:

def activities(request = None,\
            project_id = 0,\
            task_id = 0,\
            ...
activities = login_required(activities)

It is used for checking function arguments (in this case request.session), modifying arguments (it may give the function other arguments than it passes), and maybe some other stuff.

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It's a decorator, which is a special type of function (or class, in some cases) in Python that modifies another function's behavior. See this article.

@decorator
def my_func():
    pass

is really just a special syntax for

def my_func():
    pass
my_func = decorator(my_func)

---

Please check out Python Decorators Explained. It has an amazing answer that will explain everything.

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It is a decorator. It's a syntatic sugar for:

def activities(request = None,\
            project_id = 0,\
            task_id = 0,\
            ...

activities = login_required(activities)