Decorators typically use closures (including in this case), but they're really just syntax sugar for transforming one function into a different one with the same name. This code:

  @d
  def foo():
      ...

is equivalent to this code:

  def foo():
      ...
  foo = d(foo)

(You should think of a Python "def" statement as an action that creates a function and assigns it to a variable, like "foo" in this case. Since functions are first-class values, they can be sent into other functions and assigned again, which is why this works.)

But yeah, if you're implementing a decorator (a function from function to function, like "d" above), you can declare an inner function and immediately return it, and that inner function will act as a closure (it will have access to variables in the outer scope). You can take that approach in other situations as well, not just with decorators.