Code redundancy

Chris Rebert clp2 at rebertia.com
Wed Apr 21 00:29:50 CEST 2010


On Tue, Apr 20, 2010 at 2:59 PM, Alan Harris-Reid
<aharrisreid at googlemail.com> wrote:
> Stefan Behnel wrote:
>> Alan Harris-Reid, 20.04.2010 15:43:
>>> During my Python (3.1) programming I often find myself having to repeat
>>> code such as...
>>>
>>> class1.attr1 = 1
>>> class1.attr2 = 2
>>> class1.attr3 = 3
>>> class1.attr4 = 4
>>> etc.
>>>
>>> Is there any way to achieve the same result without having to repeat the
>>> class1 prefix? Before Python my previous main language was Visual
>>> Foxpro, which had the syntax...
>>>
>>> with class1
>>> .attr1 = 1
>>> .attr2 = 2
>>> .attr3 = 3
>>> .attr4 = 4
>>> etc.
>>> endwith
>>>
>>> Is there any equivalent to this in Python?
>>
>> There's more than one way to do this, depending on your actual needs and
>> the source of the attributes. I assume this is done in __init__?
>>
>> This might work for you:
>>
>>    self.__dict__.update(attr1=1, attr2=2, attr3=3, attr4=4)
>>
>> You should also think once more about the use of the code you presented
>> above, having to set all those attributes may have a little smell. Maybe
>> that's totally ok, but since you mention that you "often" find yourself
>> doing the above, you may also have a mental design problem somewhere. We
>> can't tell unless you provide a more concrete example than what you show
>> above.
>>
>> Stefan
>
> Hi Stefan, thanks for the reply.
>
> The code is not usually in class.__init__ (otherwise I would have used the
> self. prefix), but I like your self.__dict__.update(...) solution and I'll
> try and remember it.
>
> The code I was thinking of goes something like as follows (don't have a
> specific example to hand, but the principal is the same)...
>
> NewClass = BaseClass()
> NewClass.attr1 = value1
> NewClass.attr2 = value2
> NewClass.attr3 = value3
> etc.
>
> So if there are more than a couple of attributes to set for a class
> instance, how would you approach it (short of passing the values as
> parameters to BaseClass)?

Why are you against passing them as parameters?
If your constructor would have a lot of parameters, it may be a sign that:
(A) you have some Data Clumps
(http://martinfowler.com/bliki/DataClump.html) among the parameters
that ought to be made into full objects
(B) your class is doing too many things and needs to be split into
multiple classes
(http://www.refactoring.com/catalog/extractClass.html)

Cheers,
Chris
--
Yay Refactoring!
http://blog.rebertia.com



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