Configurable python decorators

README.md

Decorator class using decorator called methods to configure

Allow the behavior of a decorator to be modified by other decorators.

@mod_b
@mod_a
@base_decorator
def myfunc(): pass

In contrast to a more typical

@arg_decorator(opt_a, opt_b)
def myfunc(): pass

The motivation was a situation where a decorator was used extensively for access control checks. A new situation arose where the access control criteria needed to change for some decorated methods.

Typically this would be a case for using a decorator generator with arguments passed to configure as needed. This would have required updating every instance of the decorator to make it into a function call on the generator.

This decorator class approach allowed the existing decorators to remain unchanged and to add a configuring decorator in the handful of cases in which it was required.

Obviously there is a complexity and clarity trade-off. Perhaps time will reveal whether it is a reasonable trade.

configurable_decorator.py

from functools import update_wrapper

class decorator_class:
    def __init__(self, func):
        update_wrapper(self, func)
        self.func = func
        self.triggered = False

    def __call__(self, *args, **kwargs):
        print "I'm a decorator function"
        if self.triggered:
            print "I'm triggered"
        self.func(*args, **kwargs)
        
    def trigger_me(self):
        self.triggered = True

def trigger(decor):
    decor.trigger_me()
    return decor

@trigger
@decorator_class
def wrapme(arg1):
    """Description of wrapme"""
    print(arg1)

wrapme('boo')
# I'm a decorator function
# I'm triggered
# boo

print(wrapme.__name__)
# wrapme
print(wrapme.__doc__)
# Description of wrapme

func_decorator.py

from functools import wraps

def decorator_func(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        print "I'm a decorator function"
        func(*args, **kwargs)
        
    return wrapper

@decorator_func
def wrapme(arg1):
    """Description of wrapme"""
    print(arg1)
    
wrapme('boo')
# I'm a decorator function
# boo

print(wrapme.__name__)
# wrapme
print(wrapme.__doc__)
# Description of wrapme

help(wrapme)
# Help on function wrapme in module __main__:
#
# wrapme(*args, **kwargs)
#     Description of wrapme

simple_class_decorator.py

from functools import update_wrapper

class decorator_class:
    def __init__(self, func):
        update_wrapper(self, func)
        self.func = func

    def __call__(self, *args, **kwargs):
        print "I'm a decorator function"
        self.func(*args, **kwargs)

@decorator_class
def wrapme(arg1):
    """Description of wrapme"""
    print(arg1)

wrapme('boo')
# I'm a decorator function
# boo

print(wrapme.__name__)
# wrapme
print(wrapme.__doc__)
# Description of wrapme