[Python] ValueError: too many values to unpack (expected 2) :for batch in tqdm(dataloader,...

I used this script for my validation, what I want to do is to load multiple clips to validate my model i used Tempral transformation to obtain clips with the same size so i used this custom dataset and custom collate_fn

def collate_fn(batch):
print(f"Input batch structure: {type(batch)}, {len(batch)} elements")
for i, item in enumerate(batch):
print(f"Item {i}: {type(item)}, {len(item)} elements")

# Unpack clips and targets
batch_clips, batch_targets = zip(*batch)
print(f"Number of clips before flattening: {len(batch_clips)}")
print(f"Number of targets before flattening: {len(batch_targets)}")

# Flatten the clips and targets
batch_clips = [clip for multi_clips in batch_clips for clip in multi_clips]
batch_targets = [target for multi_targets in batch_targets for target in multi_targets]
print(f"Number of clips after flattening: {len(batch_clips)}")
print(f"Number of targets after flattening: {len(batch_targets)}")

# Stack each of them into a single tensor
batch_clips = torch.stack(batch_clips, 0)
batch_targets = torch.stack(batch_targets, 0)
print(f"Final batch_clips shape: {batch_clips.shape}")
print(f"Final batch_targets shape: {batch_targets.shape}")

return batch_clips, batch_targets

class ActionDatasetMultiClips(ActionDataset):
def __loading(self, path, frame_indices):
clips = []
for clip_frame_indices in frame_indices:
valid_indices = [i for i in clip_frame_indices if i < len(path)]
if not valid_indices:
raise ValueError(f"No valid frame indices for clip: {clip_frame_indices}")

clip = [Image.open(path).convert('RGB') for i in valid_indices]
if self.spatial_transform is not None:
self.spatial_transform.randomize_parameters()
clip = [self.spatial_transform(img) for img in clip]
clips.append(torch.stack(clip, 0))

return clips
def __getitem__(self, idx):
sequence_key = list(self.sequences.keys())[idx]
sequence_data = self.sequences[sequence_key]

frame_paths = [data['image_path'] for data in sequence_data]

# Initialize frame_indices
frame_indices = list(range(len(frame_paths)))

# Apply temporal transformation
if self.temporal_transform:
frame_indices = self.temporal_transform(frame_indices)
if isinstance(frame_indices[0], list):
frame_indices = [i for sublist in frame_indices for i in sublist]
frame_indices = [i for i in frame_indices if i < len(frame_paths)]
if not frame_indices:
raise ValueError(f"No valid frame indices for sequence {sequence_key}")

clips = self.__loading(frame_paths, [frame_indices])

action_name = sequence_data[0]['action_name']
condition = sequence_data[0]['condition']

action_name_id = self.action_name_to_id[action_name]
condition_id = self.condition_name_to_id[condition]

# Prepare one target per clip
targets = [torch.tensor([action_name_id, condition_id], dtype=torch.long) for _ in
range(len(clips))]

return clips, targets


and here is my one_epoch_validate function that I am using for validation during the training

def validate_one_epoch(model, dataloader, criterion, device):

with torch.no_grad():
for batch in tqdm(dataloader, desc="Validation", leave=False):
print(f"Batch structure in validate_one_epoch: {type(batch)}, {len(batch)} elements")
for i, item in enumerate(batch):
print(f"Item {i}: {type(item)}, shape: {item.shape if hasattr(item, 'shape') else 'N/A'}")
if len(batch) != 2:
raise ValueError(f"Expected batch to have 2 elements, but got {len(batch)}
elements")


#rest of the script

return avg_loss, action_acc, condition_acc


and this is the dataloader

def val_utils():
# spatial transformations

temporal_augmentation = []
temporal_augmentation.append(TemporalSubsampling(stride=2))
temporal_augmentation.append(TemporalEvenCrop(16, 2))
temporal_augmentation = Compose(temporal_augmentation)

val_dataset = ActionDatasetMultiClips(
annotation_path="test.csv",
spatial_transform=spatial_augmentation,
temporal_transform=temporal_augmentation,
max_sequence_length=16)

val_loader = DataLoader(
val_dataset,
batch_size=BATCH_SIZE // 2,
shuffle=True,
pin_memory=True,
num_workers=0,
collate_fn=collate_fn
)


what i expect is that each element of the batch to be a tuple of two elements the clips and their targets (2 elemnents) But for some reason the dataset is returning 4 elements instead of 2

torch.utils.data.dataloader.DataLoader'>, 4 elements
Item 0: <class 'list'>, shape: N/A
Item 1: <class 'list'>, shape: N/A
Item 2: <class 'list'>, shape: N/A
Item 3: <class 'list'>, shape: N/A


I got this error

Traceback (most recent call last):

File ~\anaconda3\envs\cnnsvm\Lib\site-packages\spyder_kernels\customize\utils.py:209 in
exec_encapsulate_locals
exec_fun(compile(code_ast, filename, "exec"), globals)

File d:\organized_files\transformer_exemple\train.py:136
val_loss, val_action_acc, val_condition_acc = validate_one_epoch(

File d:\organized_files\transformer_exemple\utils.py:92 in validate_one_epoch
frames, labels = batch # Assuming batch is a tuple of (frames, labels)# Disable gradient
computation

ValueError: too many values to unpack (expected 2) this is what i gotand what i need is
that the collate_fn returns two elements how to make sure of that

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