What kind of class does my instance belong too?

[Peter Stöhr]

Hi out there in the python-universe,

I'm having a small problem and after looking at the docs I was not able
to solve it by myself. So maybe someone out there can help me.

Lets assume I have create a class Spam and a class Eggs derived form
class Spam.
In one of the methods I have to implement a behaviours depending on
whether a passed instance is an instance of class Spam or something
different, for example:

class Spam:
    ...

class Eggs(Spam):
    def doSomething(self, aArg):
        if aArg is instance of Spam:
            self.spamIt()
        else:
            seld.doSoemthingDifferent()

What I try to figure out is what is the correct way to write such an
if-statement ?

I've tried the builtin function type(). The result <type 'instance'> is
correct bit doesn't solve my problem :-(

Thanks in advance
    Peter