fastdebug

A helpful library for improving torch and fastai errors

Install

pip install fastdebug

How to use

fastdebug is designed around improving the quality of life when dealing with Pytorch and fastai errors, while also including some new sanity checks (fastai only)

Pytorch

Pytorch now has:

• device_error
• layer_error

Both can be imported with:

from fastdebug.error.torch import device_error, layer_error

device_error prints out a much more readable error for when two tensors aren't on the same device:

inp = torch.rand().cuda()
model = model.cpu()
try:
    _ = model(inp)
except Exception as e:
    device_error(e, 'Input type', 'Model weights')

And our new log:

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-28-981e0ace9c38> in <module>()
      2     model(x)
      3 except Exception as e:
----> 4     device_error(e, 'Input type', 'Model weights')

10 frames
/usr/local/lib/python3.7/dist-packages/torch/tensor.py in __torch_function__(cls, func, types, args, kwargs)
    993 
    994         with _C.DisableTorchFunction():
--> 995             ret = func(*args, **kwargs)
    996             return _convert(ret, cls)
    997 

RuntimeError: Mismatch between weight types

Input type has type: 		 (torch.cuda.FloatTensor)
Model weights have type: 	 (torch.FloatTensor)

Both should be the same.

And with layer_error, if there is a shape mismatch it will attempt to find the right layer it was at:

inp = torch.rand(5,2, 3)
try:
    m(inp)
except Exception as e:
    layer_error(e, m)

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-84-d4ab91131841> in <module>()
      3     m(inp)
      4 except Exception as e:
----> 5     layer_error(e, m)

<ipython-input-83-ca2dc02cfff4> in layer_error(e, model)
      8     i, layer = get_layer_by_shape(model, shape)
      9     e.args = [f'Size mismatch between input tensors and what the model expects\n\n{args}\n\tat layer {i}: {layer}']
---> 10     raise e

<ipython-input-84-d4ab91131841> in <module>()
      1 inp = torch.rand(5,2, 3)
      2 try:
----> 3     m(inp)
      4 except Exception as e:
      5     layer_error(e, m)

/mnt/d/lib/python3.7/site-packages/torch/nn/modules/module.py in _call_impl(self, *input, **kwargs)
    725             result = self._slow_forward(*input, **kwargs)
    726         else:
--> 727             result = self.forward(*input, **kwargs)
    728         for hook in itertools.chain(
    729                 _global_forward_hooks.values(),

/mnt/d/lib/python3.7/site-packages/torch/nn/modules/container.py in forward(self, input)
    115     def forward(self, input):
    116         for module in self:
--> 117             input = module(input)
    118         return input
    119 

/mnt/d/lib/python3.7/site-packages/torch/nn/modules/module.py in _call_impl(self, *input, **kwargs)
    725             result = self._slow_forward(*input, **kwargs)
    726         else:
--> 727             result = self.forward(*input, **kwargs)
    728         for hook in itertools.chain(
    729                 _global_forward_hooks.values(),

/mnt/d/lib/python3.7/site-packages/torch/nn/modules/conv.py in forward(self, input)
    421 
    422     def forward(self, input: Tensor) -> Tensor:
--> 423         return self._conv_forward(input, self.weight)
    424 
    425 class Conv3d(_ConvNd):

/mnt/d/lib/python3.7/site-packages/torch/nn/modules/conv.py in _conv_forward(self, input, weight)
    418                             _pair(0), self.dilation, self.groups)
    419         return F.conv2d(input, weight, self.bias, self.stride,
--> 420                         self.padding, self.dilation, self.groups)
    421 
    422     def forward(self, input: Tensor) -> Tensor:

RuntimeError: Size mismatch between input tensors and what the model expects

Model expected 4-dimensional input for 4-dimensional weight [3, 3, 1, 1], but got 3-dimensional input of size [5, 2, 3] instead
	at layer 1: Conv2d(3, 3, kernel_size=(1, 1), stride=(1, 1))

fastai

Along with the additions above (and are used during fit), fastai now has a Learner.sanity_check function, which allows you to quickly perform a basic check to ensure that your call to fit won't raise any exceptions. They are performed on the CPU for a partial epoch to make sure that CUDA device-assist errors can be preemptively found.

To use it simply do:

from fastdebug.fastai import *
from fastai.vision.all import *

learn = Learner(...)
learn.sanity_check()

This is also now an argument in Learner, set to False by default, so that after making your Learner a quick check is ensured.

learn = Learner(..., sanity_check=True)