Resources for using custom models with trainer

Hello, I am newer to HuggingFace and wanted to create my own nn.Module class that used RoBERTa as an encoder. I am also hoping that I would be able to use it with HuggingFace’s Trainer class. Looking at the source code for Trainer, it looks like my model’s forward only needs to return an object with ouputs[loss]. Is there anything else I need to do? Are there any resources/guides/tutorials for creating your own model?

Hi @Gabe, I’m not aware of any dedicated tutorials for building custom models, but my suggestion would be to subclass PreTrainedModel (check out how e.g. BertForSequenceClassification is implemented) or one of the existing model classes. This has several advantages to using nn.Module:

  • You get all the helper methods like from_pretrained for free
  • Your custom model will play nice with the Trainer

Depending on your use case, you can also override methods directly in the Trainer - see here for a list of the available methods.

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Hi @lewtun, sorry for the late reply. Thank you for the suggestion! I have been trying that method out with subclassing the PreTrainedModel and using a separate AutoModel as an encoder for the model. I have noticed that my models from_pretrained does not seem to load the pretrained encoder. Is there any documentation/examples for this use case?

Hmm, that’s a bit odd. Would you be able to share a code snippet / Colab notebook with your workflow?

For the model/config I used:

class TagPredictionConfig(PretrainedConfig):

    def __init__(self,
                 model_type: str = "bart",
                 encoder_model: str = "facebook/bart-base",
                 num_labels: int = 5,
                 dropout: float = .5,
                 inner_dim: int = 1024,
                 max_len: int = 128,
                 unique_label_count: int = 10,
        super(TagPredictionConfig, self).__init__(num_labels=num_labels, **kwargs)
        self.model_type = model_type
        self.encoder_model = encoder_model
        self.dropout = dropout
        self.inner_dim = inner_dim
        self.max_length = max_len
        self.unique_label_count = unique_label_count
        self.intent_token = '<intent>'
        self.snippet_token = '<snippet>'
        self.columns_used = ['snippet_tokenized', 'canonical_intent', 'tags']

        encoder_config = AutoConfig.from_pretrained(
        self.vocab_size = encoder_config.vocab_size
        self.eos_token_id = encoder_config.eos_token_id

class TagPredictionModel(PreTrainedModel):
    config_class = TagPredictionConfig

    def __init__(self,
                 config: TagPredictionConfig):
        super(TagPredictionModel, self).__init__(config)
        self.config = config
        self.encoder = AutoModel.from_pretrained(self.config.encoder_model)
        self.dense_1 = nn.Linear(
        self.dense_2 = nn.Linear(
        self.dropout = nn.Dropout(self.config.dropout)

    def forward(
        encoded = self.encoder(
            # labels=labels,
        hidden_states = encoded[0]  # last hidden state

        eos_mask = input_ids.eq(self.config.eos_token_id)

        if len(torch.unique(eos_mask.sum(1))) > 1:
            raise ValueError("All examples must have the same number of <eos> tokens.")

        encoded_rep = hidden_states[eos_mask, :].view(
            hidden_states.size(0), -1, hidden_states.size(-1))[:, -1, :]

        classification_hidden = self.dropout(encoded_rep)
        classification_hidden = torch.tanh(self.dense_1(classification_hidden))
        classification_hidden = self.dropout(classification_hidden)
        logits = torch.sigmoid(self.dense_2(classification_hidden))

        loss = None
        if labels is not None:
            loss_fct = nn.BCEWithLogitsLoss()
            loss = loss_fct(logits, labels)

        return TagPredictionOutput(

Most of the code is straight from the BertForSequenceClassification model. Still, because I want to use it with T5 and a multi-label classification task, I had to modify it slightly.

The trainer is (I can give the training args, but thought it would clutter too much, so I left them out):

args_dict = TrainingArguments(**simpleTrainingArgs("./experiments/"))

    trainer = Trainer(

I think the main issue comes from the default config model name that it loads. Because when I do not set the default value for encoder_model to a real model, it errors out due to the loading of a pretrained. This happened after the first epoch because it is trying to load the best model. I can do more testing and see if it happens in more than one epoch.

@lewtun to add on through more testing, I now get the warning:

Some weights of TagPredictionModel were not initialized from the model checkpoint at ./experiments/checkpoint-40 and are newly initialized: [’.encoder.shared.weight’, ‘.encoder.encoder.embed_tokens.weight’, ‘.encoder.encoder.embed_positions.weight’, ‘.encoder.encoder.layers.0.self_attn.k_proj.weight’…(Cut for length)
You should probably TRAIN this model on a down-stream task to be able to use it for predictions and inference.

EDIT: Also, from rerunning evaluation on the validation set after training ends I am almost certain that it is not saving because the eval loss is different than during the training loop

hey @Gabe, sorry for the slow reply.

if i understand correctly, the problem you’re facing is that after the first epoch, the encoder continues to be initialised from the facebook/bart-base checkpoint - is that right?

as you suspect, i think this line might be the problem

self.encoder = AutoModel.from_pretrained(self.config.encoder_model)

because config.encoder_model would always point to whatever value you defined in the config. i wonder whether the problem can be solved by replacing AutoModel.from_pretrained with a dedicated model class like

self.encoder = BartModel(config)

this is closer to what you see in the source code for BertForSequenceClassification and (i think) ensures the model is loaded from config.json associated with each epoch’s checkpoint.