superdelegate
Delegate methods and properties to child objects in a terse, explicit style
Installation
$ pip install superdelegateConsider the motivating example of a sorted list. In order to encapsulate the list and prevent clients from breaking the sorted order, we want to only allow certain methods through to the underlying list:
import bisect
class SortedList:
def __init__(self, *args, **kwargs):
self._lst = list(*args, **kwargs)
def insert(self, elem):
bisect.insort(self._lst, elem)
def __contains__(self, elem):
ix = bisect.bisect(self._lst, elem)
return ix != len(self._lst) and self._lst[ix] == elem
def __getitem__(self, key):
return self._lst.__getitem__(key)
def __reversed__(self):
return self._lst.__reversed__()
def __len__(self):
return self._lst.__len__()
def __iter__(self):
return self._lst.__iter__()Much of that code is pretty repetitive. Can we do better? Yes! with superdelegate!
import bisect
from superdelegate import SuperDelegate, delegate_to
class SortedList(SuperDelegate):
def __init__(self, *args, **kwargs):
self._lst = list(*args, **kwargs)
def insert(self, elem):
bisect.insort(self._lst, elem)
def __contains__(self, elem):
ix = bisect.bisect(self._lst, elem)
return ix != len(self._lst) and self._lst[ix] == elem
__getitem__ = __reversed__ = __len__ = __iter__ = delegate_to('_lst')FAQs
Does it work for properties? It does work for properties!
class OnlyGrowsOlder:
def __init__(self):
self._age
@property
def age(self):
return self._age
@age.setter
def age(self, new_age):
if new_age > self._age:
self._age = new_age
else:
raise ValueError('Time is like a boy band. It only flows in one direction')
class OlderWrapper(SuperDelegate):
def __init__(self):
self._ager
age = delegate_to('_ager')Can you have multiple delgatees? You can!
class SandwichMaker:
def choose_cheese(self):
return 'swiss'
class NavyEngineer:
def lift_periscope(self):
return 'done'
class SubmarineTechnician(SuperDelegate):
def __init__(self):
self.sm = SandwichMaker()
self.ne = NavyEngineer()
choose_cheese = delegate_to('sm')
lift_periscope = delegate_to('ne')Inspiration
This library was inspired by Ruby ActiveSupport's Module#delegate extension.
