src/models/classifier.py

import lightning as L
import torch
import torch.nn.functional as F
import timm
from torch import optim
from torchmetrics import Accuracy
from torch.optim.lr_scheduler import OneCycleLR


class ImageNetClassifier(L.LightningModule):
    def __init__(self, lr: float = 1e-3):
        super().__init__()
        self.lr = lr
        #self.model = timm.create_model('resnet18', pretrained=True, num_classes=10)
        self.model = timm.create_model('resnet50', pretrained=False, num_classes=1000)
        self.train_acc = Accuracy(task="multiclass", num_classes=1000)
        self.val_acc = Accuracy(task="multiclass", num_classes=1000)
        self.save_hyperparameters()

    def forward(self, x):
        return self.model(x)

    def training_step(self, batch, batch_idx):
        x, y = batch
        logits = self(x)
        loss = F.cross_entropy(logits, y)
        preds = F.softmax(logits, dim=1)
        self.train_acc(preds, y)
        self.log("train_loss", loss, prog_bar=True, on_step=False, on_epoch=True)
        self.log("train_acc", self.train_acc, prog_bar=True, on_step=False, on_epoch=True)
        return loss

    def validation_step(self, batch, batch_idx):
        x, y = batch
        logits = self(x)
        loss = F.cross_entropy(logits, y)
        preds = F.softmax(logits, dim=1)
        self.val_acc(preds, y)
        self.log("val_loss", loss, prog_bar=True, on_step=False, on_epoch=True)
        self.log("val_acc", self.val_acc, prog_bar=True, on_step=False, on_epoch=True)

    def configure_optimizers(self):
        optimizer = torch.optim.Adam(self.parameters(), lr=self.lr)

        # Calculate total steps
        total_steps = self.trainer.estimated_stepping_batches

        scheduler = OneCycleLR(
            optimizer,
            max_lr=self.lr,
            total_steps=total_steps,
            pct_start=0.3,
            div_factor=25,
            final_div_factor=1e4,
            three_phase=False,
            anneal_strategy='cos'
        )

        return {
            "optimizer": optimizer,
            "lr_scheduler": {
                "scheduler": scheduler,
                "interval": "step"  # Update at every step
            }
        }