On 07/24/2017 08:33 AM, bruce wrote:
> Hi.
>
> I've seen sites discuss decorators, as functions that "wrap" and
> return functions.
>
> But, I'm sooo confuzed! My real question though, can a decorator have
> multiple internal functions? All the examples I've seen so far have a
> single internal function.
>
> And, if a decorator can have multiple internal functions, how would
> the calling sequence work?
>
> But as a start, if you have pointers to any really "basic" step by
> step sites/examples I can look at, I'd appreciate it. I suspect I'm
> getting flumoxed by something simple.
wrap and return are not two distinct things, they're part of the same
process... the general concept is that a decorator changes the result
of a function without modifying the function itself by returning a new
function object which does some other stuff in addition to running the
code of the original function object.
This is a really simple wrapper:
def my_decorator(some_function):
def wrapper():
print("Stuff happening before some_function() is called.")
some_function()
print("Stuff after some_function() is called.")
return wrapper
If you have an unwrapped function:
def foo():
print "This is the unwrapped function"
You can show this in action like this:
foo()
bar = my_decorator(foo)
bar()
function names are just handles to the function object, so the middle
line of those three is passing the original function object referred to
by foo to my_decorator, whose inner function returns a function object
which is runs some code before and after the original function. If the
undecorated fuction does not need to be referred to, the previous often
gets written as:
foo = my_decorator(foo)
foo()
Now to add Python's magical decorator syntax:
@my_decorator
def bar():
print "This is another unwrapped function"
bar()
So all the @my_decorator bit does is provide shorthand for the syntax
bar = my_decorator(bar)
Wasn't ultra-clear on your original question; if you wanted the
"happening before" and "happening after" to call out to other functions
instead of doing a print, you can. Is that what you mean by multiple
internal functions?
Does this clarify at all?
Do hunt some, there are some really good tutorials on decorators.
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