如何從 position 而不是名稱給出的字段值初始化 Pydantic object？

Question

我無法找到如何從 position 給出的字段值（例如在列表而不是字典中）初始化 Pydantic object 的簡單方法，所以我編寫了 class 方法positional_fields()來從可迭代對象創建所需的字典：

from typing import Optional, Iterable, Any, Dict
from pydantic import BaseModel


class StaticRoute(BaseModel):
    if_name: str
    dest_ip: str
    mask: str
    gateway_ip: str
    distance: Optional[int]
    
    @classmethod
    def positional_fields(cls, values: Iterable) -> Dict[str, Any]:
        return dict(zip(cls.__fields__, values))


input_lines = """
  route ab 10.0.0.0 255.0.0.0 10.220.196.23 1
  route gh 10.0.2.61 255.255.255.255 10.220.198.38 1
""".splitlines()

for line in input_lines:
    words = line.split()
    if words and words[0] == 'route':
        sroute = StaticRoute(**StaticRoute.positional_fields(words[1:]))
        print(sroute)

if_name='ab' dest_ip='10.0.0.0' mask='255.0.0.0' gateway_ip='10.220.196.23' distance=1
if_name='gh' dest_ip='10.0.2.61' mask='255.255.255.255' gateway_ip='10.220.198.38' distance=1

有沒有更直接的方法來實現這一目標？

我的方法期望__fields__字典的鍵按照字段在 class 中定義的順序排列。我不確定這是否得到保證（假設 Python 3.6+）。

Answer 1

改用數據類怎么樣？ 就像是：

from typing import Optional

from pydantic.dataclasses import dataclass


@dataclass
class StaticRoute:
    if_name: str
    dest_ip: str
    mask: str
    gateway_ip: str
    distance: Optional[int]


words = "route if_name dest_ip mask gateway_ip 10".split()
print(StaticRoute(*words[1:])

# StaticRoute(if_name='if_name', dest_ip='dest_ip', mask='mask', gateway_ip='gateway_ip', distance=10)

Answer 2

BaseModel類具有類方法parse_obj() ，它返回一個由字典初始化的對象實例。 類似的方法可以創建一個新方法parse_iterable() ，它返回一個由可迭代對象初始化的對象實例。

from typing import Optional, Iterable, Any, Dict
from pydantic import BaseModel


class BaseModelExt(BaseModel):
    @classmethod
    def parse_iterable(cls, values: Iterable) -> dict[str, Any]:
        return cls.parse_obj(dict(zip(cls.__fields__, values)))

    
class StaticRoute(BaseModelExt):
    if_name: str
    dest_ip: str
    mask: str
    gateway_ip: str
    distance: Optional[int]


input_lines = """
  route ab 10.0.0.0 255.0.0.0 10.220.196.23 1
  route gh 10.0.2.61 255.255.255.255 10.220.198.38 1
""".splitlines()

for line in input_lines:
    words = line.split()
    if words and words[0] == 'route':
        sroute = StaticRoute.parse_iterable(words[1:])
        print(sroute)

Answer 3

您可以使用自定義 RootType和NamedTuple的組合，如下所示：

from pydantic import BaseModel
from typing import NamedTuple, Optional


class StaticRouteTuple(NamedTuple):
    if_name: str
    dest_ip: str
    mask: str
    gateway_ip: str
    distance: Optional[int]


class StaticRoute(BaseModel):
    __root__: StaticRouteTuple

    @property
    def route(self) -> StaticRouteTuple:
        return self.__root__


input_lines = """
  route ab 10.0.0.0 255.0.0.0 10.220.196.23 1
  route gh 10.0.2.61 255.255.255.255 10.220.198.38 1
""".splitlines()

for line in input_lines:
    words = line.split()
    if words and words[0] == "route":
        sroute = StaticRoute.parse_obj(words[1:]).route
        print(sroute)

如果您不想使用自定義 RootType，您可以改用pyandic.parse_obj_as ，例如：

from pydantic import parse_obj_as
sroute = parse_obj_as(StaticRouteTuple, words[1:])