How To Make A State-Of-The-Art Deep Learning App With Fastai

Did you know it’s easy to make use of some truly excellent Python libraries to super-charge your Delphi app development on Windows? Adding Python to your toolbox of Delphi code can enhance your app development, bringing in new capabilities which help you provide innovative and powerful solutions to your app’s users, which combine the best of Python with the supreme low-code and unparalleled power of native Windows development you get with Delphi.

Are you looking for how to build a GUI for a powerful AI library? You can build a state-of-the-art deep learning solution with fastai on Delphi. This post will show you how to build a Delphi GUI app, dedicated to the fastai library.

Watch this video by Jim McKeeth, as a comprehensive introduction about why you can love both Delphi and Python at the same time:


What is the fastai library?

fastai app development on Windows

fastai is a deep learning library that provides practitioners with high-level components that can quickly and easily provide state-of-the-art results in standard deep learning domains and provides researchers with low-level components that can be mixed and matched to build new approaches. It aims to do both things without substantial compromises in ease of use, flexibility, or performance.

fastai includes:

  • A new type dispatch system for Python along with a semantic type hierarchy for tensors
  • A GPU-optimized computer vision library that can be extended in pure Python
  • An optimizer which refactors out the common functionality of modern optimizers into two basic pieces, allowing optimization algorithms to be implemented in 4–5 lines of code
  • A novel 2-way callback system that can access any part of the data, model, or optimizer and change it at any point during training
  • A new data block API
  • And much more…

And the best of it is, fastai is organized around two main design goals: to be approachable and rapidly productive, while also being deeply hackable and configurable.

fastai is built on top of a hierarchy of lower-level APIs which provide composable building blocks. This way, a user wanting to rewrite part of the high-level API or add particular behavior to suit their needs does not have to learn how to use the lowest level.

fastai app development on Windows - an image showing the layers
Hierarchy of fastai APIs.


How do I install the fastai Library?

You can easily install fastai with pip:

Or, if you are using Anaconda Python distribution, you can use this command to avoid complexities and conflicts between required libraries:


How do I build a Delphi GUI for the fastai library?

The following is the user interface structure for our project:

fastai app development on Windows -  a screenshot showing the RAD Studio IDE with a Delphi app using fastai in it
User interface structure for our fastai4D project.

Here is the list of Components used in the fastai4D demo app:

  1. TPythonEngine
  2. TPythonModule
  3. TPythonType
  4. TPythonVersions
  5. TPythonGUIInputOutput
  6. TForm
  7. TMemo
  8. TOpenDialog
  9. TSaveDialog
  10. TSplitter
  11. TImage
  12. TPanel
  13. TLabel
  14. TComboBox
  15. TButton

Navigate to the UnitFastai4D.pas, and add the following line to the FormCreate, to load our basic

fastai app development on Windows. A highlighted line showing how to use fastai
You can seamlessly load the fastai app python file inside the UnitFastai4D.pas file.

And make sure that the is in the same directory as our Fastai4D.exe or inside your Delphi project folder.

You can change the “” with any fastai script you want, or you can load your fastai scripts at runtime, by clicking the “Load script…” like we will show you in the next Demo Sections.


How to perform Deep Learning using fastai in a Delphi app?

Highly recommended practice: 

1. This GUI was created by modifying Python4Delphi Demo34, which makes us possibly change the Python version in the runtime (this will save you from the seemingly complicated dll issues).

2. Add “Jpeg” to the Uses-list at the top of our UnitMatplotlib4D.pas code. We have to do that, because otherwise, Delphi can not understand the JPG format. With this correction, it should work.

After that, the above change should look similar to this:

fastai app development on Windows - the important uses clauses in a fast ai Delphi app
Import Jpeg to your Uses-list.

And we can load JPG images into our TImage.

3. Set up these paths to your Environment Variable, for regular Python:

And set up these paths, if you use the Anaconda Python distribution:

4. To load the image dataset or to create plots, you will need to use Matplotlib in a way that is outside the “normal” command-line process. To do it, you will need to add these lines to all your Python code:

We strongly recommend you to name your image output as fastaiImage.jpg, to enable it to load automatically on your GUI after clicking the ”Show plot” button.

5. Set MaskFPUExceptions(True); to the UnitFastai4D.pas file, to avoid the Delphi raises an exception when floating operations result produce +/- infinity (e.g. division by zero) that is caused by incompatible with a number of Python libraries such as NumPy, SciPy, pandas, and Matplotlib.

One of the best parts of this Fastai4D Demo GUI is that you can choose the Python version you prefer, and it can be interchangeable.

fastai app development on Windows a fastai Delphi app screen
This GUI allows you to choose any python version installed on your system. And run the basic example by clicking the “Execute” button.

As we’ve already tested this GUI for regular Python and Anaconda Python, this Fastai4D GUI works better for regular Python distribution.

Next, click the “Execute” button to run the very basic example to download, load the image dataset, and print out their labels (the Python code is already called inside the UnitFastai4D.pas file), and click the “Show plot” button to show the figure. Here is the output:

fastai app development on Windows - a screen full of puppies
Fastai4D most basic example.


How to implement deep learning for image classification using fastai and Delphi?

Examples of implementations:

1. Load image datasets with their labels 

In this fastai embedded Python code, we are going to use the Oxford-IIIT Pet Dataset by O. M. Parkhi et al., 2012 which features 12 cat breeds and 25 dog breeds. Our model will learn how to differentiate between these 37 distinct categories. According to their paper, the best accuracy they could get in 2012 was 59.21%, using a complex model that was specific to pet detection, with separate “Image”, “Head”, and “Body” models for the pet photos.

Here is the default example embedded on the Fastai4D GUI:

fastai app development on Windows - another screen full of puppies
Use Fastai4D to load image datasets with their labels.

You can download the script here.

If you have low computational power, set up the batch size as 16 (by uncommenting this line: #bs = 16 ## Use this if you have low computational power, on this code.

2. Train deep learning model 

This example will train ResNet-34. We will use a convolutional neural network backbone and a fully connected head with a single hidden layer as a classifier. ResNet-34 is a 34 layer convolutional neural network that can be utilized as a state-of-the-art image classification model.

Illustrated below, on the right-hand side is Resnet34’s architecture where the 34 layers and the residuals from one layer to another are visualized:

fastai app development on Windows - an example showing the layers of deep learning
Illustration of ResNet-34 layer architecture on the right (visit this paper for the source).

We are building a model which will take images as input and will output the predicted probability for each of the categories (in this case, it will have 37 outputs), and we will train for 4 epochs (4 cycles through all our data).

Load the at runtime by clicking the “Load script…” button, and then “Execute”. Here is the output:

fastai app development on Windows - an image of training the AI model using a screenful of puppies
Use Fastai4D to train a deep learning model.

The code in this section will train the model for 4 epochs (4 cycles through all our data) and save the result.

If you run this without a GPU, it will need a long time to run. The following is our test on a regular CORE i5 laptop, with an onboard graphic card, and 12 Gb of RAM:

fastai app development on Windows - a screen of fastai results

3. What do the results of using fastai look like?

If you completed the deep learning model training, you would see the following results:

The result will show you the categories that the model most confused with one another. We will identify if what the model predicted was reasonable or not. In this case, the mistakes look reasonable (none of the mistakes seems obviously naive). This is an indicator that our classifier is working correctly.

fastai app development on Windows - a screenful of puppies, dogs and some kittens

The result inside Python4Delphi GUI:

fastai app development on Windows - fastai has spotted that kittens are not puppies

Furthermore, we want to plot the confusion matrix. From the confusion matrix result, we can see that the distribution is heavily skewed: The model makes the same mistakes over and over again, but it rarely confuses other categories. This suggests that it just finds it difficult to distinguish some specific categories between each other; this is a normal behavior.

fastai app development on Windows an image of the confusion matrix

The confusion matrix inside Python4Delphi GUI:

fastai app development on Windows another image of the confusion matrix

Let’s print out the most confused result, until the minimum value 2:

fastai app development on Windows printing out the confusion results

Since our model is working as we expect it to, we will unfreeze our model and train some more, and here are the results:

Plot the learning rate:

fastai app development on Windows a graph of confusion and learning

Fitting for two cycles:

fastai app development on Windows a table of results

Such a powerful deep learning library, right?

Visit this repository for the complete source code for this Fastai4Delphi project, and this repository ( for the original and more comprehensive concepts about fastai for image classification.


Are you ready to try this excellent fastai Delphi example?

Congratulations, now you have learned a lot about fastai: A state-of-the-art deep learning library, and how you can use Delphi to create a simple yet powerful GUI for it! We have learned the fundamentals of deep learning to perform image classification, and now you can explore them to boost your productivity in creating your own deep learning apps.

If you are looking for other powerful AI libraries, please read this article:

Download a free trial of RAD Studio Delphi today and try out these examples for yourself.