I need my model to accept either a bytes type variable or a string type variable and to raise an exception if any other type was passed.
from typing import Union
from pydantic import BaseModel
class MyModel(BaseModel):
a: Union[bytes, str]
m1 = MyModel(a='123')
m2 = MyModel(a=b'123')
print(type(m1.a))
print(type(m2.a))
In my case the model interprets both bytes and string as bytes.
Output:
<class 'bytes'>
<class 'bytes'>
Desired output:
<class 'str'>
<class 'bytes'>
The desired output above can be achieved if I re-assign member a:
m1 = MyModel(a='123')
m1.a = '123'
Is it possible to get it in one go?
The problem you are facing is that the str type does some automatic conversions (here in the docs):
strings are accepted as-is,
intfloatandDecimalare coerced usingstr(v),bytesandbytearrayare converted usingv.decode(), enums inheriting fromstrare converted usingv.value, and all other types cause an error
bytesare accepted as-is,bytearrayis converted usingbytes(v),strare converted usingv.encode(), andint,float, andDecimalare coerced usingstr(v).encode()
You can use StrictTypes to avoid automatic conversion between compatible types (e.g.: str and bytes):
from typing import Union
from pydantic import BaseModel, StrictStr, StrictBytes
class MyModel(BaseModel):
a: Union[StrictStr, StrictBytes]
m1 = MyModel(a='123')
m2 = MyModel(a=b'123')
print(type(m1.a))
print(type(m2.a))
Output will be as expected:
<class 'str'>
<class 'bytes'>
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