Transparently chain (combine) decorators

Question

I know this is not how decorators are intended but..

I have decorators to save various outpust from functions to xlsx, csv, other

what I want to do is

@save_xlsx
@save_csv
def whatever_function():

and have one file saved in .xlsx and the other in .csv, both working with the same output from whatever_function(). I also want to be able to use only one decorator on other functions.

Or maybe this is not the right approach?

Answer 1

This kinda reminds me of monads. Anyway, you can make a transparent generic logging decorator:

def log(callback):
    def logger(fn):
        def logwrapper(*args, **kwargs):
            value = fn(*args, **kwargs)
            callback(value)
            return value
        return logwrapper
    return logger

csv_callback = lambda x: print('writing {} to a csv file'.format(x))
xlsx_callback = lambda x: print('writing {} to an xlsx file'.format(x))

@log(csv_callback)
@log(xlsx_callback)
def test(a, b):
    return a + b

In [2]: test(1, 2)
writing 3 to an xlsx file
writing 3 to a csv file
Out[2]: 3

In [3]: test(2, 3)
writing 5 to an xlsx file
writing 5 to a csv file
Out[3]: 5

You can also just pass several callbacks into the logger to avoid excessive nesting

def log(*callbacks):
    def logger(fn):
        def logwrapper(*args, **kwargs):
            value = fn(*args, **kwargs)
            for callback in callbacks:
                callback(value)
            return value
        return logwrapper
    return logger

@log(csv_callback, xlsx_callback)
def test(a, b):
    return a + b