Live coding 13

Part 1 2022
1

This topic is for discussion of the 13th live coding session.

<<<session 12 ｜ session 14 >>>

Links from the walk-thru

What was covered

  • Using fastai on a custom new task - very flexible and interesting!!! This also prepares us for Part 2 later this year.
  • Brief discussion about “fastai unconference 2022” - watch this space.
  • (please contribute here)

Video timeline - thank you @kurianbenoy

00:00 - Introduction and Questions
05:15 - MultiTask Classification Notebook
07:40 - Good fastai tutorials
08:30 - DataBlock API
12:35 - How does ImageBlock, get_image_files work
15:15 - How is aug_transforms working
17:30 - Converting ImageDataLoaders to DataBlock
22:08 - In PyTorch DataLoaders, what happens at the last batch?
23:23 - Step2: Make DataBlock spit three things
27:30 - Modifying get_y to send as two inputs
32:00 - Looking into Dataset objects
33:50 - Can we have multiple get_items?
35:20 - Hacky notebook using data frames for creating DataBlock
39:40 - How does TransformBlock and ImageBlock works
49:30 - Looking at the source code of TransformBlock, DataBlock code
54:10 - Dataset, Dataloaders discussion
58:30 - Defining DataBlock for Multi-task classification notebook
1:05:05 - Sneak peek into how the multi-task model is trained

Detailed timestamps with summary (By @Daniel )

Walkthru 13 rough notes

11 Likes
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One thing I started doing, which I have not been doing before, is I started to capture the functionality I am 100% sure I will need down the road, but I would always need to look it up.

This gets so tedious and then you just give up and don’t even do what you know could be helpful :smile:

The most annoying thing in the world:

  • how to use subplots (though I have this memorized now maybe)
  • all the seemingly one off things but that end up super useful (how to plot a confusion matrix / correlations)

But there are also fast.ai things in that list.

So I started to use gists to capture some of the that as I am figuring out stuff for the tenth time the same month.

Really excited about this :smile: Here is for instance my gist on visualizing distributions.

Plus you can keep your gists private if you want to! Very useful :smile:

I’m thinking, if you are going through the course and are coming across stuff that is hard to remember, this approach probably can go a long way :slight_smile: I have seen students do something similar. Some of us created these repositories like this one for instance essentially doing homework :slight_smile:

But now I am hoping to extend this past the duration of the course and in a fashion more organized around reuse for other projects.

10 Likes
3

I was using a similar approach for this course, just keeping a Jupyter notebook of little snippets of code and stuff mentioned in the forums, sort of like an FAQ … but have fallen behind on it. I think the gist approach is probably better though, you can always get to it from anywhere instead of a local notebook.

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This is the most important thing to make this usable work:

https://jupyter-contrib-nbextensions.readthedocs.io/en/latest/nbextensions/gist_it/readme.html

4 Likes
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Inspired by today’s amazing walk-thru, I created this kaggle kernel.

It is based on Jeremy’s kernel for the Titanic competition, but leverages the functionality (DataBlock) that we discussed today in the walk-thru :slight_smile:

I implemented this functionality initially with just minimum fastai functionality (using datasets and dataloaders from PyTorch) and then converted it to using the DataBlock – I can’t belive how many fewer lines of code were required :smile: I think I delete like 2/3rds of the notebook :slightly_smiling_face:

The kernel processes the data using a scikit-learn pipeline (we have not covered tabular data preprocessing with fastai just yet!) and from there on feeds it to DataBlock.

Was fun working on this :slight_smile: And the walk-thru from today was super useful :pray:Hoping to continue practicing with the fastai framework :slight_smile:

Maybe someone will find this useful :slight_smile: If you would have any questions, please let me know :slight_smile:

10 Likes
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I think it was you that mentioned Obsidian?

I’ve started using it for both this course and my real job as well. I can link it across computers for free using Google Drive, and it’s searchable and can be hyperlinked both within Obsidian and to external links. It also has labels.

I’m using it for what you are describing. I have the same problem where I am constantly looking up the same thing, and when I find it I’ve forgotten all of the fine points that I figured out a year ago. This lets me constantly update the same note with small notes or pointers to myself, rather than having it scattered all over the place. It’s a bit of a time sink because I’m always making new notes, but I tell myself that it’s part of learning. I love it. If I take nothing else away from this course, that will be something valuable that I learned about, so thanks so much for mentioning it.

2 Likes
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Hi, Jeremy and fastai community.

I just wanted to say thank you for such an amazing walkthrough and course. I’ve fallen irreparably behind due to family and work commitments so I’m lagging a fair bit on the videos now, but I wanted to thank especially Jeremy but also everyone else for such a great educational experience.

I wanted to say it in person but since that’s not going to be possible I didn’t want the series to pass without extending my gratitude. I hope to be able to contribute more to the community as I learn more. (For now, I’m happy to play the role of newbie foil.)

2 Likes
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Thanks @Mark_F ! Feel free to join any walkthru sessions you like regardless of how far behind you are – always happy to answer any questions you have about earlier sessions.

4 Likes
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Thanks @Moody for reminding me to make the top post a wiki - done now.

2 Likes
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I had a doubt on what is behind the representation which gives the number and associated values in fast.ai library. During the last class, I noticed this in dls.vocab. Previously I have noticed this in get_image_files, yet after going a bit deep into it and how it works in a blogpost. I still don’t understand what is behind this output rendered in this specific shape of (#number of files) [Then contents in file] ?

image
image1373×137 50.5 KB

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I think this might be the “L” custom datatype that fast.ai library uses?

2 Likes
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#2 – this instance of L contains two object [first_list, second_list]

Imagine you have a model trained on images of ice cream. You would like your model to predict a) flavor of ice cream (one of vanilla, strawberry or chocolate) and serving size (small, large).

The vocab would look as follows:

(#2) [['vanilla', 'strawberry', 'chocolate'], ['small', 'large']]

In general, a vocab is a mapping from how the model represents labels or input tokens to a representation meaningful to us.

And sorry, if I misunderstood your question, now that I read it again – yes, this is an instance of L, which provides a superset of functionality to L (and nicer rendering).

4 Likes
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Thanks @mike.moloch and @radek for clarifying my doubt. Now I see L is the reason behind this nice rendering. I am curious to see how it really works under the hood, probably should deep dive into fastcore foundation module.

1 Like
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Timelines for youtube transcripts for this lesson:

  • 00:00 - Introduction and Questions
  • 05:15 - MultiTask Classification Notebook
  • 07:40 - Good fastai tutorials
  • 08:30 - DataBlock API
  • 12:35 - How does ImageBlock, get_image_files work
  • 15:15 - How is aug_transforms working
  • 17:30 - Converting ImageDataLoaders to DataBlock
  • 22:08 - In PyTorch DataLoaders, what happens at the last batch?
  • 23:23 - Step2: Make DataBlock spit three things
  • 27:30 - Modifying get_y to send as two inputs
  • 32:00 - Looking into Dataset objects
  • 33:50 - Can we have multiple get_items?
  • 35:20 - Hacky notebook using data frames for creating DataBlock
  • 39:40 - How does TransformBlock and ImageBlock works
  • 49:30 - Looking at the source code of TransformBlock, DataBlock code
  • 54:10 - Dataset, Dataloaders discussion
  • 58:30 - Defining DataBlock for Multi-task classification notebook
  • 1:05:05 - Sneak peek into how the multi-task model is trained
6 Likes
15

Thanks @kurianbenoy! I’ve edited your post to clean up the formatting a bit - hope that’s OK :slight_smile:

2 Likes
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Yes, that’s fine. Thank you Jeremy.

17

In addition to predicting disease and variety, we could also predict the concatenation of disease and variety, would that help the model?

With what was covered in this class, that should be easy to implement and also a good exercise. I will try tonight!

18

Hi all - I have been getting an error when starting a paperspace notebook using the Fastai image/runtime this weekend (6/18-19). Error is “Could not find the conda environment: fastai”.
I switched to the Pytorch runtime and the notebook and machine started up as usual but then I had to install the fastai dependencies.

1 Like
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Try renaming your pre-run.sh so it doesn’t get run – if that’s the cause of the problem, then you’ll be able to use fastai images after that.

1 Like
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So, my experiment did not work after all :sweat_smile: Given a learning rate of 0.1 as indicated by the learning rate finder, I get the following result with the disease error plateauing at a terrible 20%

image
image1626×924 162 KB

I suppose I was overengineering things and Jeremy’s more simple model should be able to pick up the interaction between disease and variety by itself anyway.
Now, another idea that came to mind was to use the variety as an input to the model rather than as an output like so:

dblock = DataBlock(
    blocks=(ImageBlock, CategoryBlock, CategoryBlock),
    n_inp=2,
    get_x=[lambda x: trn_path/x[1]/x[0], ColReader(2)],
    get_y=[ColReader(1)],
    splitter=RandomSplitter(0.2, seed=42),
    item_tfms=Resize(480, method='squish'),
    batch_tfms=aug_transforms(size=224, min_scale=0.75))

But I am getting a TypeError: forward() takes 2 positional arguments but 3 were given

1 Like