Python, conditional use of a decorator (package not installed in all env)

Question

I am using New Relic to monitor my Python (2.7) app, but only in my Production environment. I want to use their function_trace decorator.

In wsgi.py

try:
    import newrelic.agent
    newrelic.agent.initialize('/path/')
except Exception as e:
    pass

In views.py

if settings.ENV == "test":
    pass
else:
    import newrelic

@newrelic.agent.function_trace()
def my_function():
    ....

This works great in Production, but fails in Test, of course. I can't put if-else directly around a decorator so I was thinking that I could use a conditional decorator:

def newrelic_conditional_decorator(function)
    # What magic goes in here...
    if settings.ENV == "test":
        just return function
    else:
        use @newrelic.agent.function_trace() decorator

@newrelic_conditional_decorator
def my_function():
    ....

I'm always a bit hazy on decorators so am hoping for some help here! (Or another way to handle not having the same package in Test as in Production.)

Answer 1

A decorator takes in a function and returns a new function from it. So if you want a conditional decorator, all you need is to return the initial function when you do not want the decorator to be applied.

Your specific case

def newrelic_conditional_decorator(function):

    if settings.ENV == "test":
        # We do not apply the decorator to the function
        return function
    else:
        # We apply the decorator and return the new function
        return newrelic.agent.function_trace()(function)

@newrelic_conditional_decorator
def my_function():
    ...

A bit of generality

You could abstract this to make a more general conditional decorator which applies a given generator provided some condition function returns True.

def conditional_decorator(decorator, condition, *args):

    def wrapper(function):
        if condition(*args):
            return decorator(function)
        else:
            return function

    return wrapper

@conditional_decorator(
    newrelic.agent.function_trace(),
    lambda settings: settings.ENV != "test",
    settings)
def my_function():
    ...