How to wrap a class's methods?

[Grant Edwards]

I want to subclass an IMAP connection so that most of the
methods raise an exception if the returned status isn't 'OK'.
This works, but there's got to be a way to do it that doesn't
involve so much duplication:

class MyImap4_ssl(ima plib.IMAP4_SSL) :

def login(*args):
s,r = imaplib.IMAP4_S SL.login(*args)
if s!='OK':
raise NotOK((s,r))
return r

def list(*args):
s,r = imaplib.IMAP4_S SL.list(*args)
if s!='OK':
raise NotOK((s,r))
return r

def search(*args):
s,r = imaplib.IMAP4_S SL.search(*args )
if s!='OK':
raise NotOK((s,r))
return r

[and so on for another dozen methods]

--
Grant Edwards grante Yow! I OWN six pink
at HIPPOS!!
visi.com

[Steven Bethard]

Grant Edwards wrote:

I want to subclass an IMAP connection so that most of the
methods raise an exception if the returned status isn't 'OK'.
This works, but there's got to be a way to do it that doesn't
involve so much duplication:

class MyImap4_ssl(ima plib.IMAP4_SSL) :

def login(*args):
s,r = imaplib.IMAP4_S SL.login(*args)
if s!='OK':
raise NotOK((s,r))
return r

def list(*args):
s,r = imaplib.IMAP4_S SL.list(*args)
if s!='OK':
raise NotOK((s,r))
return r

def search(*args):
s,r = imaplib.IMAP4_S SL.search(*args )
if s!='OK':
raise NotOK((s,r))
return r

[and so on for another dozen methods]

You could try something like (Untested!):

class Wrapper(object) :
def __init__(self, func):
self.func = func
def __call__(*args, **kwargs):
self, args = args[0], args[1:]
s, r = self.func(*args )
if s != 'OK':
raise NotOK((s, r))
return r

for func_name in ['login', 'list', 'search']:
func = Wrapper(getattr (imaplib.IMAP4_ SSL, func_name))
setattr(imaplib .IMAP4_SSL, func_name, func)

STeVe

[Steven Bethard]

Grant Edwards wrote:

I want to subclass an IMAP connection so that most of the
methods raise an exception if the returned status isn't 'OK'.
This works, but there's got to be a way to do it that doesn't
involve so much duplication:

class MyImap4_ssl(ima plib.IMAP4_SSL) :

def login(*args):
s,r = imaplib.IMAP4_S SL.login(*args)
if s!='OK':
raise NotOK((s,r))
return r

def list(*args):
s,r = imaplib.IMAP4_S SL.list(*args)
if s!='OK':
raise NotOK((s,r))
return r

def search(*args):
s,r = imaplib.IMAP4_S SL.search(*args )
if s!='OK':
raise NotOK((s,r))
return r

[and so on for another dozen methods]

A more tested version of my other email:

py> class C(object):
.... def f(self, *args):
.... print "f:", args
.... def g(self, *args):
.... print "g:", args
....
py> class D(C):
.... pass
....
py> class Wrapper(object) :
.... def __init__(self, func):
.... self.func = func
.... def __call__(self, *args):
.... print "wrapped"
.... return self.func(*args )
....
py> for name in ['f', 'g']:
.... wrapper = Wrapper(getattr (C, name))
.... setattr(D, name, new.instancemet hod(wrapper, None, D))
....
py> C().f()
f: ()
py> C().g(1)
g: (1,)
py> D().f()
wrapped
f: ()
py> D().g(1)
wrapped
g: (1,)

[Grant Edwards]

On 2005-02-17, Steven Bethard <st************ @gmail.com> wrote:

py> class C(object):
... def f(self, *args):
... print "f:", args
... def g(self, *args):
... print "g:", args
...
py> class D(C):
... pass
...
py> class Wrapper(object) :
... def __init__(self, func):
... self.func = func
... def __call__(self, *args):
... print "wrapped"
... return self.func(*args )
...
py> for name in ['f', 'g']:
... wrapper = Wrapper(getattr (C, name))
... setattr(D, name, new.instancemet hod(wrapper, None, D))

Thanks. The stuff provided by the "new" module is what I was
missing.

--
Grant Edwards grante Yow! Wait... is this a FUN
at THING or the END of LIFE in
visi.com Petticoat Junction??

[Jeff Shannon]

Steven Bethard wrote:

Grant Edwards wrote:

I want to subclass an IMAP connection so that most of the
methods raise an exception if the returned status isn't 'OK'.
This works, but there's got to be a way to do it that doesn't
involve so much duplication:

class MyImap4_ssl(ima plib.IMAP4_SSL) :

def login(*args):
s,r = imaplib.IMAP4_S SL.login(*args)
if s!='OK':
raise NotOK((s,r))
return r
def list(*args):
s,r = imaplib.IMAP4_S SL.list(*args)
if s!='OK':
raise NotOK((s,r))
return r
def search(*args):
s,r = imaplib.IMAP4_S SL.search(*args )
if s!='OK':
raise NotOK((s,r))
return r
[and so on for another dozen methods]

You could try something like (Untested!):

class Wrapper(object) :
def __init__(self, func):
self.func = func
def __call__(*args, **kwargs):
self, args = args[0], args[1:]
s, r = self.func(*args )
if s != 'OK':
raise NotOK((s, r))
return r

for func_name in ['login', 'list', 'search']:
func = Wrapper(getattr (imaplib.IMAP4_ SSL, func_name))
setattr(imaplib .IMAP4_SSL, func_name, func)

You could probably also do this as a factory function, rather than as
a class (also untested!):

def Wrapper(func):
def wrapped(self, *args, **kwargs):
s, r = func(self, *args, **kwargs)
if s != 'OK':
raise NotOK((s,r))
return r
return wrapped

I believe that this will be semantically almost equivalent, but
conceptually slightly simpler.

Jeff Shannon

[Mathias Waack]

Grant Edwards wrote:

I want to subclass an IMAP connection so that most of the
methods raise an exception if the returned status isn't 'OK'.
This works, but there's got to be a way to do it that doesn't
involve so much duplication:

class MyImap4_ssl(ima plib.IMAP4_SSL) :

def login(*args):
s,r = imaplib.IMAP4_S SL.login(*args)
if s!='OK':
raise NotOK((s,r))
return r

def list(*args):
s,r = imaplib.IMAP4_S SL.list(*args)
if s!='OK':
raise NotOK((s,r))
return r

def search(*args):
s,r = imaplib.IMAP4_S SL.search(*args )
if s!='OK':
raise NotOK((s,r))
return r

[and so on for another dozen methods]

How about using a delegator:

class Wrapper:
funcs = ("login", "list", "search")
def __init__(self, classobj):
self.__wrapped = classobj()
def __getattr__(sel f, attr):
if attr in Wrapper.funcs:
def f(*args):
f1 = getattr(self.__ wrapped, attr)
s,r = f1(args)
if s != 'OK': raise NotOk((s,r))
return r
return f
# raise some exception here
imap = Wrapper(imaplib .IMAP4_SSL)

If you wrap all methods you can ignore the if-test. Instead of the
class object you can pass instances to the wrapper if you need
special arguments for initialization.

I don't like subclassing;)

Mathias

PS: note that we're wrapping the instance's methods, not the class's
methods!

[John Lenton]

On Thu, Feb 17, 2005 at 07:32:55PM +0000, Grant Edwards wrote:

I want to subclass an IMAP connection so that most of the
methods raise an exception if the returned status isn't 'OK'.
This works, but there's got to be a way to do it that doesn't
involve so much duplication:

class MyImap4_ssl(ima plib.IMAP4_SSL) :

def login(*args):
s,r = imaplib.IMAP4_S SL.login(*args)
if s!='OK':
raise NotOK((s,r))
return r

def list(*args):
s,r = imaplib.IMAP4_S SL.list(*args)
if s!='OK':
raise NotOK((s,r))
return r

def search(*args):
s,r = imaplib.IMAP4_S SL.search(*args )
if s!='OK':
raise NotOK((s,r))
return r

[and so on for another dozen methods]

something like this:

def NotOKVerified(o rig):
def f(*args):
s, r = orig(*args)
if s != 'OK':
raise NotOK((s,r))
return r
return f

class MyImap4_ssl(IMA P4_SSL):
pass

for method_name in ('login', 'list', 'search'):
setattr(MyImap4 _ssl, method_name, getattr(IMAP4_S SL, method_name))

?

I'd usually put big fat warnings around this code, and explain exaclty
why I need to do things this way...

--
John Lenton (jo**@grulic.or g.ar) -- Random fortune:
"To vacillate or not to vacillate, that is the question ... or is it?"

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[Michael Spencer]

Grant Edwards wrote:

On 2005-02-17, Steven Bethard <st************ @gmail.com> wrote:

py> class C(object):
... def f(self, *args):
... print "f:", args
... def g(self, *args):
... print "g:", args
...
py> class D(C):
... pass
...
py> class Wrapper(object) :
... def __init__(self, func):
... self.func = func
... def __call__(self, *args):
... print "wrapped"
... return self.func(*args )
...
py> for name in ['f', 'g']:
... wrapper = Wrapper(getattr (C, name))
... setattr(D, name, new.instancemet hod(wrapper, None, D))

Thanks. The stuff provided by the "new" module is what I was
missing.

No magic in the 'new' module - new.instancemet hod is just a synonym for the
method type:

import new, types
new.instancemet hod is types.MethodTyp e

True

Michael

[Grant Edwards]

On 2005-02-17, Mathias Waack <M.*****@gmx.de > wrote:

How about using a delegator:

class Wrapper:
funcs = ("login", "list", "search")
def __init__(self, classobj):
self.__wrapped = classobj()
def __getattr__(sel f, attr):
if attr in Wrapper.funcs:
def f(*args):
f1 = getattr(self.__ wrapped, attr)
s,r = f1(args)
if s != 'OK': raise NotOk((s,r))
return r
return f
# raise some exception here
imap = Wrapper(imaplib .IMAP4_SSL)

If you wrap all methods you can ignore the if-test.
I'm not, and the other methods should behave "normally":

class Wrapper:
funcs = ("login", "list", "search")
def __init__(self, classobj):
self.__wrapped = classobj()
def __getattr__(sel f, attr):
if attr in Wrapper.funcs:
def f(*args):
f1 = getattr(self.__ wrapped, attr)
s,r = f1(args)
if s != 'OK': raise NotOk((s,r))
return r
else:
f = getattr(self.__ wrapped, attr)
return f
PS: note that we're wrapping the instance's methods, not the class's
methods!

You're right.

--
Grant Edwards grante Yow! "THE LITTLE PINK
at FLESH SISTERS," I saw them
visi.com at th' FLUROESCENT BULB
MAKERS CONVENTION...

[Grant Edwards]

On 2005-02-17, Michael Spencer <ma**@telcopart ners.com> wrote:

Thanks. The stuff provided by the "new" module is what I was
missing.

No magic in the 'new' module - new.instancemet hod is just a synonym for the
method type:

>>> import new, types
>>> new.instancemet hod is types.MethodTyp e

True

Thanks -- I didn't know that either.

--
Grant Edwards grante Yow! I joined scientology
at at a garage sale!!
visi.com