Calling instance methods from a decorator

[Kirk Strauser]

I'm trying to write a decorator that would do something like:

def trace(before, after):
def middle(func):
def inner(*args, **kwargs):
func.im_self.debugfunction(before)
result = func(*args, **kwargs)
func.im_self.debugfunction(after)
return result
return inner
return middle

class Foo(object):
def __init__(self, myname):
self.name = myname

def debugfunction(self, message):
print 'Instance %s says: %s' % (self.name, message)

@trace('calling', 'finished')
def bar(self, arg):
print arg

>>Foo('snake').bar(123)

Instance snake says: calling
123
Instance snake says: finished

The gotcha seems to be that there's no way to get to 'self' from within the
"inner" function, since func will only have the "normal" attributes:

>>print dir(func)

['__call__', '__class__', '__delattr__', '__dict__', '__doc__', '__get__', '__getattribute__', '__hash__', '__init__', '__module__', '__name__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', 'func_closure', 'func_code', 'func_defaults', 'func_dict', 'func_doc', 'func_globals', 'func_name']

There's no nice im_self to bounce off of or anything. I seem to be going
about this all wrong. What's a good approach to get the desired effect?
--
Kirk Strauser
The Day Companies

[Diez B. Roggisch]

Kirk Strauser schrieb:

I'm trying to write a decorator that would do something like:

def trace(before, after):
def middle(func):
def inner(*args, **kwargs):
func.im_self.debugfunction(before)
result = func(*args, **kwargs)
func.im_self.debugfunction(after)
return result
return inner
return middle

class Foo(object):
def __init__(self, myname):
self.name = myname

def debugfunction(self, message):
print 'Instance %s says: %s' % (self.name, message)

@trace('calling', 'finished')
def bar(self, arg):
print arg

>>>Foo('snake').bar(123)

Instance snake says: calling
123
Instance snake says: finished

The gotcha seems to be that there's no way to get to 'self' from within the
"inner" function, since func will only have the "normal" attributes:

>>>print dir(func)

['__call__', '__class__', '__delattr__', '__dict__', '__doc__', '__get__', '__getattribute__', '__hash__', '__init__', '__module__', '__name__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', 'func_closure', 'func_code', 'func_defaults', 'func_dict', 'func_doc', 'func_globals', 'func_name']

There's no nice im_self to bounce off of or anything. I seem to be going
about this all wrong. What's a good approach to get the desired effect?

Of course you can get the self - just use the first paramter, because it
*is* self. Self is just a parameter - nothing special.

Alternatively, declare inner like this:

def inner(self, *args, **kwargs):
...
try:
return func(self, *args, **kwargs)
finally:
....
Note the additional try/finally. It's got nothing todo with your
original problem - but you should use it to guarantee that your trace
gets called when leaving the call.

Diez

[Kirk Strauser]

At 2008-05-30T17:40:17Z, "Diez B. Roggisch" <de***@nospam.web.dewrites:

Of course you can get the self - just use the first paramter, because it
*is* self. Self is just a parameter - nothing special.

If I blame it on being a long week, can I keep my geek card?
--
Kirk Strauser
The Day Companies