如何在 Python3/Pydantic 中定义具有互斥成员/字段的 class

Question

I have a class called GeoLocation with fields (point and region) that are mutually exclusive. How do I define the class?

Python3 code:

from enum import Enum
from typing import Optional
from pydantic import BaseModel

class Point(BaseModel):
    latitude: float
    longitude: float

class Ellipse(BaseModel):
    center: Point
    semiMajorAxis: Optional[float] = None

# point and region are mutually exclusive. Exactly one must be present.
class GeoLocation(BaseModel):
    point:Ellipse
    region:Polygon
    confidence: Optional[int] = None

Expected json output after serialization:

{
"location": {
      "point": {
       "center": {"latitude": 37.0, "longitude": -101.3}
              }
       }
}

How do I define the GeoLocation class in python3 or pydantic such that point and region are mutually exclusive? I was able to implement this in Rust by defining an enum of with two struct as shown below.

Rust Code

#[derive(Serialize, Deserialize, Debug)]
#[serde(rename_all = "lowercase")]
pub enum Loc {
    Point(Ellipse),
    Region(Polygon),
}

#[derive(Serialize, Deserialize, Debug)]
pub struct GeoLocation {
    #[serde(flatten)]
    pub loc: Loc, // point and region are  mutually exclusive

    #[serde(skip_serializing_if = "Option::is_none")]
    pub confidence: Option<Int>, // OPTIONAL
}

Can I define an enum of classes in python3? Something like the following code. If yes, how do I initialize Loc

class Ellipse(BaseModel):
    center: Point
    semiMajorAxis: Optional[float] = None

class Polygon(BaseModel):
    exterior: Point

# Note: point and region are mutually exclusive.  
# Exactly one must be present.
class Loc(Enum):
    point = Ellipse
    region = Polygon

class GeoLocation(BaseModel):
    loc: Loc
    confidence: Optional[int] = None

Thanks

Answer 1

Since you have the loc field as an enum value, this wouldn't be any different from using the Union typing class (or in Python 3.10, using the typing or operator, | ).

class GeoLocation(BaseModel):
    loc: Union[Ellipse, Polygon]  # loc: Ellipse | Polygon,

This should give you the same structure as in your Rust example.