Is there are good DRY fix for this painful design pattern?
Jugurtha Hadjar
jugurtha.hadjar at gmail.com
Tue Feb 27 13:56:50 EST 2018
On 02/26/2018 03:41 PM, 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?
>
>
> Thanks,
>
>
>
def snatchit(func):
def snatched(self, *args, **kwargs):
frame = inspect.signature(func)
for name in frame.parameters:
if name != 'self':
kwargs.setdefault(name, getattr(self, name))
return func(self, *args, **kwargs)
snatched.__name__ = func.__name__
snatched.__doc__ = func.__doc__
return snatched
class Foo(object):
def __init__(self, sleepy, groggy):
self.sleepy = sleepy
self.groggy = groggy
@snatchit
def spam(self, sleepy=None):
print("I am spam. sleepy=", sleepy)
@snatchit
def ham(self, sleepy=None, groggy=None):
print("I am ham. sleepy=", sleepy, " and groggy=", groggy)
>>> f = Foo(1, 19)
>>> f.spam()
I am spam. sleepy= 1
>>> f.spam(sleepy=8)
I am spam. sleepy= 8
>>> f.ham(sleepy=8)
I am ham. sleepy= 8 and groggy= 19
>>> f.ham(sleepy=17, groggy=888)
I am ham. sleepy= 17 and groggy= 888
--
~ Jugurtha Hadjar,
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