Define a polymorph Marshmallow schema in Python

Consider we have the UserSchema which contains two attributes of name and user. The issue is that I am looking for a solution to load AdminSchema or GuestSchema based on the type attribute of MainSchema.

class MainSchema(Schema):    type = fields.Str()class AdminSchema(MainSchema):    role = fields.Str(required=True)class GuestSchema(MainSchema):    reason = fields.Str(required=True)class UserSchema(Schema):    name = fields.Str(required=True)    user = fields.Nested(MainSchema, required=True)

This is a sample data.

[   {"name": "john","user":{"type": "admin","role": "sales"      }   },   {"name": "jane","user":{"type": "guest","reason": "visitor"      }   }]

This is an example of the problem. I am already aware of the PolyField which I can not use for this case.