Add extra arguments to side_effects in python Mock

Question

from unittest.mock import patch

def get_title():
    return 'title'


def get_msg():
    return 'msg'


def do_log(title, msg):
    sys.stderr.write(get_title(),
                     get_msg())
    return


def myfunction():
    title = get_title()
    msg = get_msg()
    do_log(title, msg)


def my_new_do_log(*args, **kwargs):
    '''
    we know, args = title, msg
    But I want add EXTRA arguments, 
    like handler (from caller / from controller)
    '''
    sys.stderr.write(get_title(),
                     get_msg(),
                     handler.get_author_from_handler()
                     )
    # Note: handler is argument from controller!


@patch('do_log')
def controller(handler, mock_do_log):
    mock_do_log.side_effect = my_new_do_log
    myfunction()


if __name__ == '__main__':
    controller(handler)

So how pass "handler" (a extra argument) to my_new_do_log?

if i try something like:

mock_do_log.side_effect = my_new_do_log(handler)

I lost arguments from my context manager (title and msg). Is it possible append extra arguments to context manager.

Answer 1

You can define a new callable in controller() and use it as side effect. The simple and neat way to do it is to use lambda function:

@patch('do_log')
def controller(handler, mock_do_log):
    mock_do_log.side_effect = lambda *args,**kwargs:my_new_do_log(handler,*args,**kwargs)
    myfunction()

where my_new_do_log() signature become

def my_new_do_log(handler, *args, **kwargs):
    ....

You can either define a new explicit function to do it

@patch('do_log')
def controller(handler, mock_do_log):
    def handler_log(*args,**kwargs):
        my_new_do_log(handler,*args,**kwargs)
    mock_do_log.side_effect = handler_log
    myfunction()

But my taste is for the lambda version.

---

The question about context manager is little bit confused : you don't have any context manager in your example but just a patch decorator that behave like context manager. Anyway I think you can iterate my suggestion to take in account how many arguments you want.