decorating decorators: try to get my head around understanding it

def upper(f):
    @wrap
    def uppercase(*args, **kargs):
        a,b = f(*args, **kargs)
        return a.upper(), b.upper()
    return uppercase

A decorator in Python

 @foo
 def bar(...): ...

is just equivalent to

 def bar(...): ...
 bar = foo(bar)

You want to get the effect of

@wrap
@upper
def hello(): ....

i.e.

hello = wrap(upper(hello))

so the wrap should be called on the return value of upper:

def upper_with_wrap(f):
   def uppercase(...): ...
   return wrap(uppercase)

which is also equivalent to applying the decorator on that function:

def upper_with_wrap(f):
   @wrap
   def uppercase(...): ...
   # ^ equivalent to 'uppercase = wrap(uppercase)'
   return uppercase