What is the difference between @foobar and @foobar()?

The @foobar decorator is applied to a function or class using an instance of the decorator itself, foobar. The @foobar() decorator calls the factory function foobar, which should return a decorator object (an instance of a callable class or a function), which is then applied to the function or class.

Example:

# Decorator without parameters
def simple_decorator(func):
    def wrapper(*args, **kwargs):
        print("Executing simple decorator")
        return func(*args, **kwargs)
    return wrapper

@simple_decorator
def my_function():
    print("Executing my_function")

# my_function() is equivalent to simple_decorator(my_function)()

# Decorator with parameters
def decorator_factory(param):
    def actual_decorator(func):
        def wrapper(*args, **kwargs):
            print(f"Executing decorator with param: {param}")
            return func(*args, **kwargs)
        return wrapper
    return actual_decorator

@decorator_factory("example_param")
def another_function():
    print("Executing another_function")

# another_function() is equivalent to decorator_factory("example_param")(another_function)() - first the factory is called, then the resulting decorator

Comparison table:

	@foobar	@foobar()
Execution	The foobar object itself is used as a decorator.	Calls foobar (factory), and the result is used as a decorator.
Parameters	The decorator does not accept parameters directly.	Allows passing parameters to the decorator factory.
Flexibility	Less flexible if decorator customization is needed.	More flexible, allows creating parameterized decorators.