change dataclass to frozen at runtime

[jpanico]

I'm working with a dataclass that is code-generated by a tool I do not control:

@dataclass
class Concern:
    id: ConcernID

Note that the dataclass is not declared as frozen. I need this class to be frozen for the sake of Hashability, so I would like to modify the class at **runtime** to make it frozen. Is this possible?

thanks,

Joe

[Yoriz]

I think you might have to create a new frozen version of the unfrozen dataclass at the most efficient point you can in your code.

[snippsat]

Could do someting like this.

from dataclasses import dataclass, make_dataclass, fields

class ConcernID:
    '''a example of how ConcernID class could be'''
    def __init__(self, value):
        self.value = value

    def __str__(self):
        return self.value

    def __repr__(self):
        return f"ConcernID({self.value})"

@dataclass
class Concern:
    id: ConcernID

# Create a frozen version of the class at runtime
FrozenConcern = make_dataclass(
    'FrozenConcern',
    fields=[(f.name, f.type) for f in fields(Concern)],
    frozen=True
)

concern_id = ConcernID(123)
not_frozen = Concern(id=concern_id)
frozen_concern = FrozenConcern(id=concern_id)

If test will now frozen=True property prevents any changes to the instance attributes,ensuring immutability.

>>> not_frozen.id = 456
>>> not_frozen.id
456
>>> 
>>> frozen_concern.id = 456
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
  File "<string>", line 4, in __setattr__
dataclasses.FrozenInstanceError: cannot assign to field 'id'