function wrappers

[Ramon Crehuet]

Dear all,
I have a Fortran programming background and I have some difficulties in 
understading how function wrappers work. I have delved into the subject 
because of the new decorators, but I understand the decorator syntax. My 
ignorance is more profound... Here is an example without decorators:

def require_int(func):
       def wrapper(arg):
           assert isinstance(arg, int)
           return func(arg)
       return wrapper
p1(a):
   print a

p2=require_int(p1)

My question is: why do p2 arguments become wrapper arguments? What is 
the flux of the arguments in the program when you pass functions as 
arguments?
I have looked into some books and google but I cannot find a 
satisfactory explanation. Could somebody please give me a hint or point 
me to an appropriate source?
Thanks for your time,

Ramon