Storing a callback function as a class member
in [Python]
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From: Nathan Huesken on 7 Jul 2010 17:48 Hi, I have a class, where I want to store a callback function as a member to access later: class CallbackClass: def setCallback(self,cb): self.cb = cb def callCallback(self, para): self.cb(para) Doing so, I get the error: callbackFunc() takes exactly 1 parameter (2 given) self is given as parameter this way, is it not? How can this be done? Thanks! Nathan
From: MRAB on 7 Jul 2010 18:09 Nathan Huesken wrote: > Hi, > > I have a class, where I want to store a callback function as a member > to access later: > > class CallbackClass: > def setCallback(self,cb): > self.cb = cb > > def callCallback(self, para): > self.cb(para) > > Doing so, I get the error: > callbackFunc() takes exactly 1 parameter (2 given) > > self is given as parameter this way, is it not? How can this be done? > Could you provide a short program which we could run to reproduce the problem?
From: Rhodri James on 7 Jul 2010 18:23 On Wed, 07 Jul 2010 22:48:11 +0100, Nathan Huesken <python(a)lonely-star.org> wrote: > Hi, > > I have a class, where I want to store a callback function as a member > to access later: > > class CallbackClass: > def setCallback(self,cb): > self.cb = cb > > def callCallback(self, para): > self.cb(para) > > Doing so, I get the error: > callbackFunc() takes exactly 1 parameter (2 given) > > self is given as parameter this way, is it not? How can this be done? rhodri(a)gnudebst:~$ python Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> class CBClass: .... def set_cb(self, cb): .... self.cb = cb .... def call_cb(self, para): .... self.cb(para) .... >>> def trivial(arg): .... print arg .... >>> c = CBClass() >>> c.set_cb(trivial) >>> c.call_cb("Hello, world") Hello, world Works for me. Which version of Python are you using? -- Rhodri James *-* Wildebeeste Herder to the Masses
From: Emile van Sebille on 7 Jul 2010 18:31 On 7/7/2010 2:48 PM Nathan Huesken said... > class CallbackClass: > def setCallback(self,cb): > self.cb = cb > > def callCallback(self, para): > self.cb(para) > You'll have to show how you're invoking this -- the following works for me (ie, I don't get an error): class CallbackClass: def setCallback(self,cb): self.cb = cb def callCallback(self, para): self.cb(para) a = CallbackClass() def test(param): return 2*param a.setCallback(test) a.callCallback(3) Emile
From: Ian Kelly on 7 Jul 2010 20:35
On Wed, Jul 7, 2010 at 3:48 PM, Nathan Huesken <python(a)lonely-star.org> wrote: > Hi, > > I have a class, where I want to store a callback function as a member > to access later: > > class CallbackClass: > def setCallback(self,cb): > self.cb = cb > > def callCallback(self, para): > self.cb(para) > > Doing so, I get the error: > callbackFunc() takes exactly 1 parameter (2 given) > > self is given as parameter this way, is it not? How can this be done? No, self will not be passed as a parameter. A function is only treated as a method when it is present in the class dict. If it is in the instance dict as you have above, then it's just a normal function. If you want it to receive self in this case, then you should have your callCallback method pass it in explicitly. HTH, Ian |