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Re: Accessing class attribute

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  Re: Accessing class attribute Peter Otten <__peter__@web.de> - 2013-09-12 09:04 +0200

#54039 — Re: Accessing class attribute

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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