Accessing class attribute
Peter Otten
__peter__ at web.de
Thu Sep 12 03:04:26 EDT 2013
Peter Otten wrote:
> chandan kumar wrote:
>
>> Hi ,
>>
>> I'm new to python ,please correct me if there is any thing wrong with the
>> way accessing class attributes.
>>
>> Please see the below code .I have inherited confid in ExpectId class,
>> changed self.print_msg to Hello. Now inherited confid in TestprintmsgID
>> class.Now I wanted to print self.print_msg value (which is changed under
>> ExpectId class) as Hello under TestprintmsgID. I end up with error
>> saying
>> TestprintmsgID has no attribute self.print_msg. Atleast i expect the
>> null to be printed.
>>
>>
>>
>> class confid():
>> def __init__(self):
>> self.print_msg = ""
>>
>> class ExpectId(confid):
>>
>> def __init__(self):
>> self.print_msg = " Hello"
>>
>> def expectmethod(self):
>> print "self.print_mesg = ",self.print_msg
>>
>> class TestprintmsgID(confid):
>>
>> def __init__(self):
>> "Created Instance"
>>
>> def printmsgmethod(self):
>> print "printmsgmethod print_msg val = ",self.print_msg---- Here
>> is
>> the Attribute error
>
> If the class has an __init__() method the initializer of the base class is
> not invoked automatically.
>
> In the above code the initializer of TestprintmsgId does nothing, so you
> can avoid it. ExpectId.__init__() however must invoke confid.__init_().
>
> The complete example:
Sorry, my examples don't show what I wanted to show. I assumed a class
hierarchy
confid <-- ExpectId <-- TestprintmsgId
Also, ExpectId.__init__() need not invoke confid.__init__() in this
particular case because both set the same attribute.
The general ideas however still stand:
(1) if you write an __init__() method it should invoke the __init__() method
of the baseclass.
(2) omit no-op __init__() methods altogether.
Again, sorry for the confusion!
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