how to do a conditional decorator in python

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.

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)

How about:

def foo():   ...if doing_performance_analysis:   foo = timeit(foo)

I imagine you could even wrap this into a decorator that would take a boolean flag and another decorator, and would only apply the latter if the flag is set to True:

def cond_decorator(flag, dec):   def decorate(fn):      return dec(fn) if flag else fn   return decorate@cond_decorator(doing_performance_analysis, timeit)def foo():   ...