Python: Quick and dirty datatypes (DTO)

Question

Very often, I find myself coding trivial datatypes like

class Pruefer:     def __init__(self, ident, maxNum=float('inf'), name=""):         self.ident  = ident         self.maxNum = maxNum         self.name   = name 

While this is very useful (Clearly I don't want to replace the above with anonymous 3-tuples), it's also very boilerplate.

Now for example, when I want to use the class in a dict, I have to add more boilerplate like

    def __hash__(self):         return hash(self.ident, self.maxNum, self.name) 

I admit that it might be difficult to recognize a general pattern amongst all my boilerplate classes, but nevertheless I'd like to as this question:

• Are there any popular idioms in python to derive quick and dirty datatypes with named accessors?

• Or maybe if there are not, maybe a Python guru might want to show off some metaclass hacking or class factory to make my life easier?

Answer 1

>>> from collections import namedtuple >>> Pruefer = namedtuple("Pruefer", "ident maxNum name") >>> pr = Pruefer(1,2,3) >>> pr.ident 1 >>> pr.maxNum 2 >>> pr.name 3 >>> hash(pr) 2528502973977326415 

To provide default values, you need to do little bit more... Simple solution is to write subclass with redefinition for __new__ method:

>>> class Pruefer(namedtuple("Pruefer", "ident maxNum name")): ...     def __new__(cls, ident, maxNum=float('inf'), name=""): ...         return super(Pruefer, cls).__new__(cls, ident, maxNum, name) ...  >>> Pruefer(1) Pruefer(ident=1, maxNum=inf, name='') 

Answer 2

One of the most promising things from with Python 3.6 is variable annotations. They allow to define namedtuple as class in next way:

In [1]: from typing import NamedTuple  In [2]: class Pruefer(NamedTuple):    ...:     ident: int    ...:     max_num: int    ...:     name: str    ...:       In [3]: Pruefer(1,4,"name") Out[3]: Pruefer(ident=1, max_num=4, name='name') 

It same as a namedtuple, but is saves annotations and allow to check type with some static type analyzer like mypy.

Update: 15.05.2018

Now, in Python 3.7 dataclasses are present so this would preferable way of defining DTO, also for backwardcompatibility you could use attrs library.