Pydantic：允许突变，禁止改变类型答案

【问题标题】：Pydantic: allow mutation, forbid to change typesPydantic：允许突变，禁止改变类型
【发布时间】：2021-04-19 18:33:36
【问题描述】：

有什么方法可以禁止改变变异 Pydantic 模型的类型？例如，

from pydantic import BaseModel

class AppConfig(BaseModel):

    class Config:
        allow_mutation = True
    
    a: int = 33
    b: float = 22.0

我希望能够更改字段，例如：

config = AppConfig()
config.a = 44

但我想禁止更改字段的类型，例如：

config.a = '44'
<Some error message here>

【问题讨论】：

标签： python types pydantic

【解决方案1】：

理解 Pydantic 的一个关键点是它会尝试强制到你注释的类型。例如。它会尝试在您为a 提供的任何输入上调用int。如果您不想要这种行为，请使用strict types：

In [1]: from pydantic import BaseModel, StrictInt, StrictFloat
   ...:
   ...: class AppConfig(BaseModel):
   ...:
   ...:     class Config:
   ...:         allow_mutation = True
   ...:
   ...:     a: StrictInt = 33
   ...:     b: StrictFloat = 22.0
   ...:

In [2]: AppConfig(a=42, b=0.0)
Out[2]: AppConfig(a=42, b=0.0)

In [3]: AppConfig(a='42', b=0.0)
---------------------------------------------------------------------------
ValidationError                           Traceback (most recent call last)
<ipython-input-3-702f4ffeef8d> in <module>
----> 1 AppConfig(a='42', b=0.0)

~/opt/miniconda3/envs/wrangle/lib/python3.7/site-packages/pydantic/main.cpython-37m-darwin.so in pydantic.main.BaseModel.__init__()

ValidationError: 1 validation error for AppConfig
a
  value is not a valid integer (type=type_error.integer)

此外，默认情况下，pydantic 不会对属性的分配执行验证，要更改您需要在 Config 中设置 validate_assignment 的行为，因此您需要：

In [1]: from pydantic import BaseModel, StrictInt, StrictFloat
   ...:
   ...: class AppConfig(BaseModel):
   ...:
   ...:     class Config:
   ...:         allow_mutation = True
   ...:         validate_assignment = True
   ...:
   ...:     a: StrictInt = 33
   ...:     b: StrictFloat = 22.0
   ...:

In [2]: config = AppConfig()

In [3]: config
Out[3]: AppConfig(a=33, b=22.0)

In [4]: config.a = '42'
---------------------------------------------------------------------------
ValidationError                           Traceback (most recent call last)
<ipython-input-4-39b2a238b39e> in <module>
----> 1 config.a = '42'

~/opt/miniconda3/envs/wrangle/lib/python3.7/site-packages/pydantic/main.cpython-37m-darwin.so in pydantic.main.BaseModel.__setattr__()

ValidationError: 1 validation error for AppConfig
a
  value is not a valid integer (type=type_error.integer)

【讨论】：