Way to extend context of function? for example in decorator

Question

As for example if want let decorated function see logger from closure

def logged(func):
    #here i want create logger which i want to be available from decorated function.
    @wraps(func)
    def _logged(*args, **kwargs):
        
        return func(*args,**kwargs)
        #naive idea hot to do it - obviously doesn't work
        #return exec('func(*args,**kwargs)',dict(func=func,logger=logger,args=args,kwargs=kwargs),dict(func=func,logger=logger,args=args,kwargs=kwargs))
    return _logged

Answer 1

Here's (another) way to do it, but again it's not through a closure which are determined at compile time, so can't be added at runtime. This version adds a global variable to the function's global namespace, taking care to save and restore the value of any similarly named variable that was already there. I got the idea from @Martijn Pieters' answer to the somewhat related question: How to inject variable into scope with a decorator?

from functools import wraps


class Logger:
    def __call__(self, *args, **kwargs):
        return print(*args, **kwargs)


def logged(func):
    logger = Logger()  # Get or create value to be added.
    varname = 'logger'
    sentinel = object()

    @wraps(func)
    def _logged(*args, **kwargs):
        namespace = func.__globals__
        oldvalue = namespace.get(varname, sentinel)  # Save prev value.
        namespace[varname] = logger

        try:
            return func(*args, **kwargs)
        finally:
            if oldvalue is sentinel:
                del namespace[varname]
            else:
                namespace[varname] = oldvalue

    return _logged


@logged
def myfunc():
    logger('Logged from myfunc.')


myfunc()  # -> Logged from myfunc.