i need a module for more involved command line parsing

[DeaD_EyE]

To understand a decorator, you have to understand what a closure is.

def function(a):
    b = 40
    def inner_function():
        print(a,b)
    inner_function()  # <-- calls the inner_function
    # inner function has access to the scope of function

If you rewrite the inner_function as anonymous lambda function, it's more clear:

def function(a):
    b = 40
    inner_function = lambda: print(a, b)
    inner_function()  # <-- calls the inner_function
    # inner function has access to the scope of function

Decorators should take a function and modify the behavior (input_values, return_values).
This can be reached with a closure, which returns the inner function.

def square(function):
    def inner(*args, **kwargs):
        return function(*args, **kwargs) ** 2
    return inner # <- returns the inner function without calling it


def foo():
    return 42


print(foo())
# the direct call together with the decorator looks like this
square(foo)()  # <- square(foo) returns inner, inner is called
# assign the decorated function to a name
square_foo = square(foo) # square_foo is now the function inner
# calling square_foo
square_foo()

To @ sign for the decorator is just a syntactical sugar for us.

@wrapper
def func():
    return

# is the same like
def func():
    return
func = wrapper(func)
# old name is overwritten by inner function