Is there are good DRY fix for this painful design pattern?
Rhodri James
rhodri at kynesim.co.uk
Mon Feb 26 10:28:54 EST 2018
On 26/02/18 14:41, Steven D'Aprano wrote:
> I have a class with a large number of parameters (about ten) assigned in
> `__init__`. The class then has a number of methods which accept
> *optional* arguments with the same names as the constructor/initialiser
> parameters. If those arguments are None, the defaults are taken from the
> instance attributes.
>
> An example might be something like this:
>
>
> class Foo:
> def __init__(self, bashful, doc, dopey, grumpy,
> happy, sleepy, sneezy):
> self.bashful = bashful # etc
>
> def spam(self, bashful=None, doc=None, dopey=None,
> grumpy=None, happy=None, sleepy=None,
> sneezy=None):
> if bashful is None:
> bashful = self.bashful
> if doc is None:
> doc = self.doc
> if dopey is None:
> dopey = self.dopey
> if grumpy is None:
> grumpy = self.grumpy
> if happy is None:
> happy = self.happy
> if sleepy is None:
> sleepy = self.sleepy
> if sneezy is None:
> sneezy = self.sneezy
> # now do the real work...
>
> def eggs(self, bashful=None, # etc...
> ):
> if bashful is None:
> bashful = self.bashful
> # and so on
>
>
> There's a lot of tedious boilerplate repetition in this, and to add
> insult to injury the class is still under active development with an
> unstable API, so every time I change one of the parameters, or add a new
> one, I have to change it in over a dozen places.
>
> Is there a good fix for this to reduce the amount of boilerplate?
You could use dicts? Untested code:
class Foo:
def __init__(self, **kwds):
self.defaults = kwds
def spam(self, **kwds):
vars = self.defaults.copy()
vars.update(kwds)
# Do the work with vars['bashful'] etc
--
Rhodri James *-* Kynesim Ltd
More information about the Python-list
mailing list