How to create a Python decorator that can be used either with or without parameters?

Question

I\'d like to create a Python decorator that can be used either with parameters:

@redirect_output(\"somewhere.log\")
def foo():
    ....

or

Answer 1

Several answers here already address your problem nicely. With respect to style, however, I prefer solving this decorator predicament using functools.partial, as suggested in David Beazley's Python Cookbook 3:

from functools import partial, wraps

def decorator(func=None, foo='spam'):
    if func is None:
         return partial(decorator, foo=foo)

    @wraps(func)
    def wrapper(*args, **kwargs):
        # do something with `func` and `foo`, if you're so inclined
        pass

    return wrapper

While yes, you can just do

@decorator()
def f(*args, **kwargs):
    pass

without funky workarounds, I find it strange looking, and I like having the option of simply decorating with @decorator.

As for the secondary mission objective, redirecting a function's output is addressed in this Stack Overflow post.

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If you want to dive deeper, check out Chapter 9 (Metaprogramming) in Python Cookbook 3, which is freely available to be read online.

Some of that material is live demoed (plus more!) in Beazley's awesome YouTube video Python 3 Metaprogramming.

Happy coding :)