Question

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Understanding Python decorators

What does a Python decorator do? And where can I see the codes that are running when I add a decorator to a method?

For example, when I add @login_required at the top of a method, does any code replace that line? How exactly does this line check the user session?

Answer 1

when I add @login_required at the top of a method, does any code replace that line?

Kind of. Adding @login_required before your view function has the same effect as doing this:

def your_view_function(request):
    # Function body

your_view_function = login_required(your_view_function)

For explanations of decorators in Python, see:

• http://www.python.org/dev/peps/pep-0318/
• http://wiki.python.org/moin/PythonDecorators#What_is_a_Decorator

So decorator functions accept an original function, and return a function that (probably) calls the original function, but does something else too.

In the case of login_required, I think it checks the request object passed to view functions to see if the user is authenticated.