MethodType/FunctionType and decorators

Alex Popescu the.mindstorm.mailinglist at gmail.com
Thu Jul 5 01:17:33 CEST 2007


On Jul 5, 1:52 am, Alex Popescu <the.mindstorm.mailingl... at gmail.com>
wrote:
> Hi all!
>
> I am pretty new to Python, so please excuse me if I am missing
> something. Lately, I've been playing with decorators and I am a bit
> confused about some behavior. Here is the code that puzzles me:
>
> in python shell:
>
> def function():
>   pass
>
> class A(object):
>   def method(self):
>     pass
>
> from types import MethodType
> from types import FunctionType
>
> if type(function) is FunctionType:
>   print "this is what I expect"
>
> if type(A.method) is MethodType:
>   print "this is what I expect"
>
> so far so good... everything seems logical.
>
> But if a decorator is declared things are becoming different:
>
> def deco(function):
>   if type(function) is MethodType:
>     print "MethodType"
>   elif type(function) is FunctionType:
>     print "FunctionType"
>
> @deco
> def function2():
>   pass
>
> # ==> this prints out FunctionType (oke)
>
> class A(object):
>   @deco
>   def method(self):
>     pass
>
> # ==> this prints out FunctionType (???)
>
> Can somebody shed some light on why I am seeing this?
>
> (Using Python 2.5.1 on Win XP).
>
> TIA,
>
> ./alex
> --
> .w( the_mindstorm )p.

First of all I should correct my example to use
isinstance(function_or_method, builtin_factory_function).

Secondly, I guess what is happening is the following:

- when testing from outside the class definition, the function is
already attached to the class instance and this is the reason why its
type is instancemethod
- for decorators, my test is executed before the class is defined and
so at that moment the function is still a function; it will become a
methodinstance only after the class definition is closed

Is this correct or am I just fabulating here?

TIA,

./alex
--
.w( the_mindstorm )p.





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