Transforms are not compatible with DownloadedDatasets

[ShownX]

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Description

Transforms are not compatible with _DownloadedDatasets such as MNIST

Environment info (Required)

MAC and Ubuntu 16.04

What to do:
1. Download the diagnosis script from https://github.com/ghraw/apache/incubator-mxnet/master/tools/diagnose.py
2. Run the script using `python diagnose.py` and paste its output here.

Package used (Python/R/Scala/Julia):
(I'm using Python)

Error Message:

TypeError: forward() takes 2 positional arguments but 3 were given

Minimum reproducible example

from mxnet.gluon.data import Dataloader
from mxnet.gluon.vision import transforms, MNIST

ds = MNIST(train=True, transform=transforms.ToTensor)
dl = DataLoader(ds, 10, shuffle=True)

What have you tried to solve it?

the transforms function take one data as input but _DownloadDatasets use datasets and labels as input L201

Also, checked the ImageRecordDataset, it consists with _DownloadedDatasets.
Suggest to change the transform API to forward(F, x, y)

[piiswrong]

It's not supposed to work that way. You need to use a lambda

[ShownX]

Hmm..., I do not think it is a good idea to use lambda or another function to do the data augmentation since there are transform functions. Can I ask what is the reason to keep difference? I think the customer would get confused and frustrated when using this features.

[szha]

I labeled the issue this way as I think we should eventually get rid of the redundant transform argument in datasets.