How to reduce the DRY violation in this code

[Lorenzo Sutton]

On 27/09/2016 17:49, Steve D'Aprano wrote:
> I have a class that takes a bunch of optional arguments. They're all
> optional, with default values of various types. For simplicity, let's say
> some are ints and some are floats:
>
>
> class Spam:
>     def __init__(self, bashful=10.0, doc=20.0, dopey=30.0,
>                  grumpy=40, happy=50, sleepy=60, sneezy=70):
>         # the usual assign arguments to attributes dance...
>         self.bashful = bashful
>         self.doc = doc
>         # etc.
>
>
> I also have an alternative constructor that will be called with string
> arguments.

May I ask: do you really need to add this method? Can't you ensure that 
the data passed during initialisation is already of the right type (i.e. 
can you convert to float/ints externally)? If now why?

Lorenzo.

It converts the strings to the appropriate type, then calls the
> real constructor, which calls __init__. Again, I want the arguments to be
> optional, which means providing default values:
>
>
>     @classmethod
>     def from_strings(cls, bashful='10.0', doc='20.0', dopey='30.0',
>                      grumpy='40', happy='50', sleepy='60', sneezy='70'):
>         bashful = float(bashful)
>         doc = float(doc)
>         dopey = float(dopey)
>         grumpy = int(grumpy)
>         happy = int(happy)
>         sleepy = int(sleepy)
>         sneezy = int(sneezy)
>         return cls(bashful, doc, dopey, grumpy, happy, sleepy, sneezy)
>
>
> That's a pretty ugly DRY violation. Imagine that I change the default value
> for bashful from 10.0 to (let's say) 99. I have to touch the code in three
> places (to say nothing of unit tests):
>
> - modify the default value in __init__
> - modify the stringified default value in from_strings
> - change the conversion function from float to int in from_strings
>
>
> Not to mention that each parameter is named seven times.
>
>
> How can I improve this code to reduce the number of times I have to repeat
> myself?
>
>
>
>
>