问题描述
我正在尝试创建 timedelta 的子类,该子类期望接收毫秒而不是秒,但目前无法正常工作。
我是不是违背了原则?使用 Pydantic 是否有“正确”的方法来实现这一目标?或者我是否需要告诉 Pydantic Millisecondtimedelta
只是一个 timedelta
..
from datetime import timedelta
from pydantic import BaseModel
class Millisecondtimedelta(timedelta):
@classmethod
def __get_validators__(cls):
# timedelta expects seconds
yield lambda v: v / 1000
yield cls
class MyModel(BaseModel):
td: Millisecondtimedelta
data = {
"td": 7598040,}
print(MyModel(**data))
结果:
Traceback (most recent call last):
File "main.py",line 14,in <module>
class MyModel(BaseModel):
File "pydantic/main.py",line 262,in pydantic.main.ModelMetaclass.__new__
File "pydantic/fields.py",line 315,in pydantic.fields.ModelField.infer
File "pydantic/fields.py",line 284,in pydantic.fields.ModelField.__init__
File "pydantic/fields.py",line 362,in pydantic.fields.ModelField.prepare
File "pydantic/fields.py",line 541,in pydantic.fields.ModelField.populate_validators
File "pydantic/class_validators.py",line 255,in pydantic.class_validators.prep_validators
File "pydantic/class_validators.py",line 238,in pydantic.class_validators.make_generic_validator
File "/usr/lib/python3.8/inspect.py",line 3105,in signature
return Signature.from_callable(obj,follow_wrapped=follow_wrapped)
File "/usr/lib/python3.8/inspect.py",line 2854,in from_callable
return _signature_from_callable(obj,sigcls=cls,File "/usr/lib/python3.8/inspect.py",line 2384,in _signature_from_callable
raise ValueError(
ValueError: no signature found for builtin type <class '__main__.Millisecondtimedelta'>
解决方法
如 on the doc page of __get_validators__()
所示,您需要产生一个或多个验证器。
修改后的类报告如下;问题是 Pydantic 理解(对于 timedelta 字段)int 并浮动为秒 (source)。
class MillisecondTimedelta(timedelta):
@classmethod
def __get_validators__(cls):
yield cls.validate
@classmethod
def validate(cls,v):
if any(isinstance(v,t) for t in (int,float)):
return cls(milliseconds=v)
现在一切正常。
>>> data = {"td": 1000}
>>> print(MyModel(**data))
td=MillisecondTimedelta(seconds=1)
编辑:没有自定义类和验证器,可以使用函数来编辑要分配给类构造函数的值;需要装饰这个函数,as seen here
class MyModel(BaseModel):
td: timedelta
@validator('td')
def convert_to_ms(cls,v):
return v / 1000
此解决方案也有效:
>>> data = {"td": 3000}
>>> print(MyModel(**data))
td=datetime.timedelta(seconds=3)
,
啊哈,原来我需要改变两件事。
-
实际上从验证器返回一个
timedelta
,我返回的是cls
,它是我的自定义子类。 -
不要继承
timedelta
from datetime import timedelta
from pydantic import BaseModel
class MillisecondTimedelta:
@classmethod
def __get_validators__(cls):
yield lambda v: timedelta(milliseconds=v)
class MyModel(BaseModel):
td: MillisecondTimedelta
data = {
"td": 7598040,}
print(repr(MyModel(**data)))
MyModel(td=datetime.timedelta(seconds=7598,microseconds=40000))