用更复杂的类型替换内置类型。 蟒蛇

Question

I want to create a replacement class of the built-in type set that can be constructed exactly like set. Inheritance must not be used because some functions are removed to trigger method not found exceptions. This class is also used to find places where there might be implicit type conversions of the built-in python collection types.

class SetFacade:

    def __init__(self, iterable):
        self.lst = list(iterable)

    # other allowed member functions...

The problem with this constructor definition is, that I cant call the constructor SetFacade() without arguments.

How can I create a constructor that behaves exactly like the built-in set?

Thus it must allow

• SetFacade([a,c,b])
• SetFacade([])
• SetFacade()

Answer 1

Define exactly ...

The best way to create a set-like class is to derive from collections.Set . You'll need to implement __len__ , __iter__ and __contains__ .

To be able to add element, derive from collections.MutableSet instead and implement add and discard .

Answer 2

Inherit from set :

>>> class SetFacade(set):
...     pass
...
>>> SetFacade([1,2,3,4])
SetFacade([1, 2, 3, 4])
>>> SetFacade([1,2,3,3])
SetFacade([1, 2, 3]

Answer 3

if you want to have an empty constructor...

class SetFacade:

def __init__(self, iterable=None):
    if iterable is None: 
         iterable = []
    self.lst = list(iterable)