how to do a conditional decorator in python

Question

Is it possible to decorator a function conditionally. For example, I want to decorate the function foo() with a timer function (timeit) only doing_performance_analysis is True (see the psuedo-code below).

if doing_performance_analysis:   @timeit   def foo():     """     do something, timeit function will return the time it takes     """     time.sleep(2) else:   def foo():     time.sleep(2)   

Answer 1

Decorators are simply callables that return a replacement, optionally the same function, a wrapper, or something completely different. As such, you could create a conditional decorator:

def conditional_decorator(dec, condition):     def decorator(func):         if not condition:             # Return the function unchanged, not decorated.             return func         return dec(func)     return decorator 

Now you can use it like this:

@conditional_decorator(timeit, doing_performance_analysis) def foo():     time.sleep(2)   

The decorator could also be a class:

class conditional_decorator(object):     def __init__(self, dec, condition):         self.decorator = dec         self.condition = condition      def __call__(self, func):         if not self.condition:             # Return the function unchanged, not decorated.             return func         return self.decorator(func) 

Here the __call__ method plays the same role as the returned decorator() nested function in the first example, and the closed-over dec and condition parameters here are stored as arguments on the instance until the decorator is applied.

Answer 2

A decorator is simply a function applied to another function. You can apply it manually:

def foo():    # whatever    time.sleep(2)  if doing_performance_analysis:     foo = timeit(foo)