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jbranchaud
48 lines
1.4 KiB
Markdown
48 lines
1.4 KiB
Markdown
# Avoid Modification With Frozen Dataclass
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The `@dataclass` decorator can be set as _frozen_ to prevent modification of
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values on instances of that `dataclass`.
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Without making it frozen, I can easily subvert validations by changing the value
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of attributes after the `__post_init__` validations are called.
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```python
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>>> config = BPEConfig(300, []) # passes validations
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>>> config.vocab_size = 22 # this is invalid, wish this was prevented
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```
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Here is the updated `@dataclass` declaration with `frozen=True` passed as a
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parameter.
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```python
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from dataclasses import dataclass
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from typing import ClassVar
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@dataclass(frozen=True)
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class BPEConfig:
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BASE_VOCAB_SIZE: ClassVar[int] = 256
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vocab_size: int
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special_tokens: list[str]
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def __post_init__(self):
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if self.vocab_size < self.BASE_VOCAB_SIZE:
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msg = f"vocab_size ({self.vocab_size}) must be greater than or equal to BASE_VOCAB_SIZE ({self.BASE_VOCAB_SIZE})"
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raise ValueError(msg)
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```
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Now I am prevented from modifying a scalar value like `vocab_size` after the
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instance has been created.
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```python
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>>> config = BPEConfig(300, [])
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>>> config.vocab_size = 22
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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File "<string>", line 4, in __setattr__
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dataclasses.FrozenInstanceError: cannot assign to field 'vocab_size'
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```
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This doesn't prevent you from modifying the contents of attributes that are
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`list` or `dict` types.
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