# Is it correct to replace a class after self.post\_init() function?

**URL:** <https://discuss.huggingface.co/t/is-it-correct-to-replace-a-class-after-self-post-init-function/16332>\
**Category:** 🤗Transformers\
**Created:** [March 31, 2022, 4:15pm UTC](https://discuss.huggingface.co/t/is-it-correct-to-replace-a-class-after-self-post-init-function/16332 "2022-03-31T16:15:16Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![khangnguyen2907](https://avatars.discourse-cdn.com/v4/letter/k/779978/32.png) [@khangnguyen2907](https://discuss.huggingface.co/u/khangnguyen2907)\
**Post date:** [March 31, 2022, 4:15pm UTC](https://discuss.huggingface.co/t/is-it-correct-to-replace-a-class-after-self-post-init-function/16332/1 "2022-03-31T16:15:16Z")

</div>

I am using BartModel. However, My project is using a 3-dimensional attention mask that is not accepted by BartModel (I already tried to input my attention mask with the size of [batch, seq\_length, seq\_length] and it pulls out errors) and `position_ids` that is not an argument when using BartModel. Therefore, I add some codes in `_expand_mask()` function, fix something in `BartLearnedPositionalEmbedding()` class, and `BartModel` class to be suitable for my project. Because `BartEncoder` and `BartDecoder` class have `_expand_mask` function and `BartLearnedPositionalEmbedding()` class, I overrided them to replace `self.embed_positions` instance with my class that I have already fixed as below:

```python
class My_BartEncoder(BartEncoder):
    def __init__ (self, config: BartConfig, embed_tokens: Optional[nn.Embedding] = None):
        super(). __init__ (config, embed_tokens)
        embed_dim = config.d_model
        self.embed_positions = BartLearnedPositionalEmbedding(
            config.max_position_embeddings, 
            embed_dim
        )

```

and also add `position_ids` argument to `forward` function because I need it for my new `BartLearnedPositionalEmbedding` (I did not change the name of the class, just modify the code). And do the same thing with `BartDecoder` class. Finally, I change `self.encoder` and `self.decoder` in `BartModel` class with `My_BartEncoder` and `My_BartDecoder` as I do above.

I want to ask whether I am doing right, I read that `self.post_init()` is executed at the end. However, I inherited `BartModel` then replace 2 instances like that

```python
class My_BartModel(BartModel):
    def __init__ (self, config: BartConfig):
        super(). __init__ (config)
        self.encoder = My_BartEncoder(config, self.shared)
        self.decoder = My_BartDecoder(config, self.shared)

```

is it legal? And second, I use another names that are not `BartEncoder` and `BartDecoder`, so when I initialize model by using `from_pretrained`, is there any errors or the weights can not recognize the class to put the weights into it? I am a newbie and grateful when you help me.