Pass multiple arguments to a decorator in Python

Question

I am trying to build a flask app which will be having RBAC feature. For this I have written a decorator which is working fine but it can only take one argument meaning only one access level(e.g WRITE, READ, admin etc), but I want to pass multiple arguments to it. I have tried passing a list but its not taking it. I have never worked with decorators so need help with it. Thanks.

def permission_required(permission):
 def decorator(f):
 @wraps(f)
 def decorated_function(*args, **kwargs):
 if not current_user.can(permission):
 abort(403)
 return f(*args, **kwargs)
 return decorated_function
 return decorator
def admin_required(f):
 return permission_required(Permission.ADMIN)(f)

I as passing it like this:

@role_needed(Permission.VIEW), but I want to have this @role_needed(Permission.VIEW, Permission.WRITE)

My permission class is like this:

class Permission:
 VIEW = 'Vew'
 WRITE = 'Write'
 ADMIN = 'admin'

• Alain T.: What do you mean by "its not taking it" ?

Answer 1

First, I'd advise that you have a look at some tutorial on decorators, they are pretty cool and you definitely need to understand the basics if you want to use flask. I personally quite like this RealPython tutorial.

Second, you have two solutions : either default second argument or argument packing.

def permission_required(permission1, permission2=None):
...

or

def permission_required(*perms):
...

I personaly way prefer the second option. Example:

def permission_required(*perms):
 def decorator(f):
 @wraps(f)
 def decorated_function(*args, **kwargs):
 for perm in perms:
 if not current_user.can(perm):
 abort(403)
 return f(*args, **kwargs)
 return decorated_function
 return decorator

• Sandipan: Yes, you are rightthe article cleared my doubt, I wonder how come I didn't come across it before. Thanks a lot. I fixed the issue
• Big Bro: Glad it helped ;)

Answer 2

I think you missed the point that decorators are just usual functions, taking a function in argument and another one, the later being by design a wrapper around the original one. In your case, permission_required is a decorator factory, that can be used to specialize a decorator based on input arguments. So all you need to do is to allow passing any number of arguments to your decorator factory:

def role_needed(*permissions):
 def decorator(f):
 @wraps(f)
 def decorated_function(*args, **kwargs):
 nonlocal permissions # Just to make sure `permission` is available in this scope
 # Implement here how to deal with permissions
 return f(*args, **kwargs)
 return decorated_function
 return decorator

which can be called as intended:

@role_needed(Permission.VIEW, Permission.WRITE, ...)

In the function, permissions will store the input Permission as a Python tuple object.

• Sandipan: Thanks for the answer. Yup I missed that part that is just another python function.