pydantic 字段的默认值设置获取当前时间 python

pydantic 字段的默认值如何设置获取当前时间
这种情况不要使用 default，而要用 default_factory
关于这两种的区别说明如下:

: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.

来看看错误的例子，即通过 default 获取当前时间：

from datetime import datetime, timezone from pydantic import BaseModel, Field from typing import Optional import 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)

可以看到两个时间是一样的

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

再来看看 default_factory：

from datetime import datetime, timezone from pydantic import BaseModel, Field from typing import Optional import 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)

【pydantic 字段的默认值设置获取当前时间】可以看到，两个时间相距了 1 秒钟