Oops, I forgot the link. It should show up shortly at https://www.python.org/dev/peps/pep-0557/.

Eric.

On 9/8/17 7:57 AM, Eric V. Smith wrote:

I've written a PEP for what might be thought of as "mutable namedtuples
with defaults, but not inheriting tuple's behavior" (a mouthful, but it
sounded simpler when I first thought of it). It's heavily influenced by
the attrs project. It uses PEP 526 type annotations to define fields.
>From the overview section:

@dataclass
class InventoryItem:
    name: str
    unit_price: float
    quantity_on_hand: int = 0

    def total_cost(self) -> float:
        return self.unit_price * self.quantity_on_hand

Will automatically add these methods:

  def __init__(self, name: str, unit_price: float, quantity_on_hand: int
= 0) -> None:
      self.name = name
      self.unit_price = unit_price
      self.quantity_on_hand = quantity_on_hand
  def __repr__(self):
      return
f'InventoryItem(name={self.name!r},unit_price={self.unit_price!r},quantity_on_hand={self.quantity_on_hand!r})'

  def __eq__(self, other):
      if other.__class__ is self.__class__:
          return (self.name, self.unit_price, self.quantity_on_hand) ==
(other.name, other.unit_price, other.quantity_on_hand)
      return NotImplemented
  def __ne__(self, other):
      if other.__class__ is self.__class__:
          return (self.name, self.unit_price, self.quantity_on_hand) !=
(other.name, other.unit_price, other.quantity_on_hand)
      return NotImplemented
  def __lt__(self, other):
      if other.__class__ is self.__class__:
          return (self.name, self.unit_price, self.quantity_on_hand) <
(other.name, other.unit_price, other.quantity_on_hand)
      return NotImplemented
  def __le__(self, other):
      if other.__class__ is self.__class__:
          return (self.name, self.unit_price, self.quantity_on_hand) <=
(other.name, other.unit_price, other.quantity_on_hand)
      return NotImplemented
  def __gt__(self, other):
      if other.__class__ is self.__class__:
          return (self.name, self.unit_price, self.quantity_on_hand) >
(other.name, other.unit_price, other.quantity_on_hand)
      return NotImplemented
  def __ge__(self, other):
      if other.__class__ is self.__class__:
          return (self.name, self.unit_price, self.quantity_on_hand) >=
(other.name, other.unit_price, other.quantity_on_hand)
      return NotImplemented

Data Classes saves you from writing and maintaining these functions.

The PEP is largely complete, but could use some filling out in places.
Comments welcome!

Eric.

P.S. I wrote this PEP when I was in my happy place.

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