Python 之 Bunch Pattern

When prototyping (or even finalizing) data structures such as trees, it can be useful to have a flexible class that will allow you to specify arbitrary attributes in the constructor. In these cases, the “Bunch” pattern (named by Alex Martelli in the Python Cookbook) can come in handy. There are many ways of implementing it, but the gist of it is the following:(实现数据结构，好比说树的时候使用，有多种实现方式，要点以下)

class Bunch(dict):
    def __init__(self, *args, **kwds):
        super(Bunch, self).__init__(*args, **kwds)
        self.__dict__ = self

There are several useful aspects to this pattern. First, it lets you create and set arbitrary ttributes by supplying them as command-line arguments:（这个pattern颇有用，第一，你可一设置任意的属性）

>>> x = Bunch(name="Jayne Cobb", position="Public Relations")
>>> x.name
'Jayne Cobb'

Second, by subclassing dict, you get lots of functionality for free, such as iterating over the keys/attributes or easily checking whether an attribute is present. Here’s an example:（第二，经过子类化的dict，你能够得到不少功能，好比迭代的key-value，或者检查属性值是否存在等）

>>> T = Bunch
>>> t = T(left=T(left="a", right="b"), right=T(left="c"))
>>> t.left
{'right': 'b', 'left': 'a'}
>>> t.left.right
'b'
>>> t['left']['right']
'b'
>>> "left" in t.right
True
>>> "right" in t.right
False

This pattern isn’t useful only when building trees, of course. You could use it for any situation where you’d want a flexible object whose attributes you could set in the constructor.（不单单用于建树）