any ways to judge whether an object is initilized or not in a class

[James Stroud]

momobear wrote:
> hi, I am puzzled about how to determine whether an object is
> initilized in one class, anyone could give me any instructions?
> here is an example code:
> 
> class coffee:
>          def  boil(self):
>                self.temp = 80
> 
> a = coffer()
> if a.temp > 60:
>      print "it's boiled"
> 
> in C++ language we must initilized a variable first, so there is no
> such problem, but in python if we don't invoke a.boil(), we will not
> get self.temp to be initilized, any way to determine if it's initilzed
> before self.temp be used.
> 

I think you might be looking for hasattr:

class coffee:
   def boil(self):
     if hasattr(self, 'temp') and self.temp > 60:
       print "Its boilt, yo."
     else:
       self.temp = 80

Other ways to do this are try/except:


class coffee:
   def boil(self):
     try:
       if self.temp > 60:
         print "Its bizzle, yo."
         return
     except AttributeError:
       pass
     self.temp = 80


Which is not so good in my opinion because it takes too much typing and 
makes your fingers hurt at the very tips.

A fun way is with dict.setdefault which might actually be cleanest, but 
you loose testing the precondition for the print:

class coffee:
   def boil(self):
     if self.__dict__.setdefault('temp', 80) > 60:
       print "Its bizzle m'wizzle."


py> c = coffee()
py> c.temp
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
AttributeError: coffee instance has no attribute 'temp'
py> c.boil()
Its bizzle m'wizzle.
py> c.temp
80


Of course, the idea is that, in classes, you will be intimately aware of 
the attributes of your class via __init__, as others have mentioned, so 
you should never really resort to any of the above.

James