Python Cookbook

Collecting a Bunch of Named Items

Credit: Alex Martelli

Problem

You want to collect a bunch of items together, naming each item of the bunch, and you find dictionary syntax a bit heavyweight for the purpose.

Solution

Any (classic) class inherently wraps a dictionary, and we take advantage of this:

class Bunch:
    def _ _init_ _(self, **kwds):
        self._ _dict_ _.update(kwds)

Now, to group a few variables, create a Bunch instance:

point = Bunch(datum=y, squared=y*y, coord=x)

You can access and rebind the named attributes just created, add others, remove some, and so on. For example:

if point.squared > threshold:
    point.isok = 1

Discussion

Often, we just want to collect a bunch of stuff together, naming each item of the bunch; a dictionary’s okay for that, but a small do-nothing class is even handier and is prettier to use.

A dictionary is fine for collecting a few items in which each item has a name (the item’s key in the dictionary can be thought of as the item’s name, in this context). However, when all names are identifiers, to be used just like variables, the dictionary-access syntax is not maximally clear:

if point['squared'] > threshold

It takes minimal effort to build a little class, as in this recipe, to ease the initialization task and provide elegant attribute-access syntax:

if bunch.squared > threshold

An equally attractive alternative implementation to the one used in the solution is:

class EvenSimplerBunch:
    def _ _init_ _(self, **kwds): self._ _dict_ _ = kwds

The alternative presented ...