What does a Python decorator do, and where is its code?
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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?
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:
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.
A decorator is in effect a function wrapping another function or class. The function behind the decorator in your case is named login_required . Look in your imports to find it.
A decorator is a function which wraps another function. Say you have a function f(x) and you have a decorator h(x), the decorator function takes as argument your function f(x) and so in effect what you will have is a new function h(f(x)). It makes for cleaner code as for instance in your login_required, you do not have to put in the same code to test if a user is logged in rather you can wrap the function in a login_required function so that such a function is called only if the user is logged in. Study this snippet below
def login_required(restricted_func):
"""Decorator function for restricting access to restricted pages.
Redirects a user to login page if user is not authenticated.
Args:
a function for returning a restricted page
Returns:
a function
"""
def permitted_helper(*args, **kwargs):
"""tests for authentication and then call restricted_func if
authenticated"""
if is_authenticated():
return restricted_func(*args, **kwargs)
else:
bottle.redirect("/login")
return permitted_helper
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