关于python:pydantic-字段的默认值设置获取当前时间

pydantic 字段的默认值如何设置获取以后工夫

这种状况不要应用 default，而要用 default_factory
对于这两种的区别阐明如下:

:param default: since this is replacing the field’s default, its first argument is used      to set the default, use ellipsis (``...``) to indicate the field is required:param default_factory: callable that will be called when a default value is needed for this field      If both `default` and `default_factory` are set, an error is raised.

来看看谬误的例子，即通过 default 获取以后工夫：

from datetime import datetime, timezonefrom pydantic import BaseModel, Fieldfrom typing import Optionalimport timedef get_utc_now_timestamp() -> datetime:    return datetime.utcnow().replace(tzinfo=timezone.utc)class Struct(BaseModel):    releaseDate: Optional[datetime] = Field(        default=get_utc_now_timestamp()    )print(Struct().releaseDate)time.sleep(1)print(Struct().releaseDate)

能够看到两个工夫是一样的

2022-01-27 14:16:23.876755+00:002022-01-27 14:16:23.876755+00:00

再来看看 default_factory：

from datetime import datetime, timezonefrom pydantic import BaseModel, Fieldfrom typing import Optionalimport timedef get_utc_now_timestamp() -> datetime:    return datetime.utcnow().replace(tzinfo=timezone.utc)class Struct(BaseModel):    releaseDate: Optional[datetime] = Field(        default_factory=get_utc_now_timestamp    )print(Struct().releaseDate)time.sleep(1)print(Struct().releaseDate)

能够看到，两个工夫相距了 1 秒钟

2022-01-27 14:15:55.195409+00:002022-01-27 14:15:56.200775+00:00