January 22, 2019

1480 words 7 mins read



The fastai deep learning library, plus lessons and tutorials

repo name fastai/fastai
repo link https://github.com/fastai/fastai
homepage http://docs.fast.ai
language Jupyter Notebook
size (curr.) 449824 kB
stars (curr.) 17314
created 2017-09-09
license Apache License 2.0

Build Status pypi fastai version Conda fastai version

Anaconda-Server Badge fastai python compatibility fastai license


The fastai library simplifies training fast and accurate neural nets using modern best practices. See the fastai website to get started. The library is based on research into deep learning best practices undertaken at fast.ai, and includes "out of the box" support for vision, text, tabular, and collab (collaborative filtering) models. For brief examples, see the examples folder; detailed examples are provided in the full documentation. For instance, here’s how to train an MNIST model using resnet18 (from the vision example):

from fastai.vision import *
path = untar_data(MNIST_PATH)
data = image_data_from_folder(path)
learn = cnn_learner(data, models.resnet18, metrics=accuracy)

Note for course.fast.ai students

This document is written for fastai v1, which we use for the current version the course.fast.ai deep learning courses. If you’re following along with a course at course18.fast.ai (i.e. the machine learning course, which isn’t updated for v1) you need to use fastai 0.7; please follow the installation instructions here.


NB: fastai v1 currently supports Linux only, and requires PyTorch v1 and Python 3.6 or later. Windows support is at an experimental stage: it should work fine but it’s much slower and less well tested. Since Macs don’t currently have good Nvidia GPU support, we do not currently prioritize Mac development.

fastai-1.x can be installed with either conda or pip package managers and also from source. At the moment you can’t just run install, since you first need to get the correct pytorch version installed - thus to get fastai-1.x installed choose one of the installation recipes below using your favorite python package manager. Note that PyTorch v1 and Python 3.6 are the minimal version requirements.

It’s highly recommended you install fastai and its dependencies in a virtual environment (conda or others), so that you don’t interfere with system-wide python packages. It’s not that you must, but if you experience problems with any dependency packages, please consider using a fresh virtual environment just for fastai.

Starting with pytorch-1.x you no longer need to install a special pytorch-cpu version. Instead use the normal pytorch and it works with and without GPU. But you can install the cpu build too.

If you experience installation problems, please read about installation issues.

If you are planning on using fastai in the jupyter notebook environment, make sure to also install the corresponding packages.

More advanced installation issues, such as installing only partial dependencies are covered in a dedicated installation doc.

Conda Install

conda install -c pytorch -c fastai fastai

This will install the pytorch build with the latest cudatoolkit version. If you need a higher or lower CUDA XX build (e.g. CUDA 9.0), following the instructions here, to install the desired pytorch build.

Note that JPEG decoding can be a bottleneck, particularly if you have a fast GPU. You can optionally install an optimized JPEG decoder as follows (Linux):

conda uninstall --force jpeg libtiff -y
conda install -c conda-forge libjpeg-turbo pillow==6.0.0
CC="cc -mavx2" pip install --no-cache-dir -U --force-reinstall --no-binary :all: --compile pillow-simd

If you only care about faster JPEG decompression, it can be pillow or pillow-simd in the last command above, the latter speeds up other image processing operations. For the full story see Pillow-SIMD.

PyPI Install

pip install fastai

By default pip will install the latest pytorch with the latest cudatoolkit. If your hardware doesn’t support the latest cudatoolkit, follow the instructions here, to install a pytorch build that fits your hardware.

Bug Fix Install

If a bug fix was made in git and you can’t wait till a new release is made, you can install the bleeding edge version of fastai with:

pip install git+https://github.com/fastai/fastai.git

Developer Install

The following instructions will result in a pip editable install, so that you can git pull at any time and your environment will automatically get the updates:

git clone https://github.com/fastai/fastai
cd fastai
pip install -e ".[dev]"

Next, you can test that the build works by starting the jupyter notebook:

jupyter notebook

and executing an example notebook. For example load examples/tabular.ipynb and run it.

Please refer to CONTRIBUTING.md and Notes For Developers for more details on how to contribute to the fastai project.

Building From Source

If for any reason you can’t use the prepackaged packages and have to build from source, this section is for you.

  1. To build pytorch from source follow the complete instructions. Remember to first install CUDA, CuDNN, and other required libraries as suggested - everything will be very slow without those libraries built into pytorch.

  2. Next, you will also need to build torchvision from source:

    git clone https://github.com/pytorch/vision
    cd vision
    python setup.py install
  3. When both pytorch and torchvision are installed, first test that you can load each of these libraries:

    import torch
    import torchvision

    to validate that they were installed correctly

    Finally, proceed with fastai installation as normal, either through prepackaged pip or conda builds or installing from source (“the developer install”) as explained in the sections above.

Installation Issues

If the installation process fails, first make sure your system is supported. And if the problem is still not addressed, please refer to the troubleshooting document.

If you encounter installation problems with conda, make sure you have the latest conda client (conda install will do an update too):

conda install conda

Is My System Supported?

  1. Python: You need to have python 3.6 or higher

  2. CPU or GPU

    The pytorch binary package comes with its own CUDA, CuDNN, NCCL, MKL, and other libraries so you don’t have to install system-wide NVIDIA’s CUDA and related libraries if you don’t need them for something else. If you have them installed already it doesn’t matter which NVIDIA’s CUDA version library you have installed system-wide. Your system could have CUDA 9.0 libraries, and you can still use pytorch build with CUDA 10.0 libraries without any problem, since the pytorch binary package is self-contained.

    The only requirement is that you have installed and configured the NVIDIA driver correctly. Usually you can test that by running nvidia-smi. While it’s possible that this application is not available on your system, it’s very likely that if it doesn’t work, then you don’t have your NVIDIA drivers configured properly. And remember that a reboot is always required after installing NVIDIA drivers.

  3. Operating System:

    Since fastai-1.0 relies on pytorch-1.0, you need to be able to install pytorch-1.0 first.

    As of this moment pytorch.org’s 1.0 version supports:

    Platform GPU CPU
    linux binary binary
    mac source binary
    windows binary binary

    Legend: binary = can be installed directly, source = needs to be built from source.

    If there is no pytorch preview conda or pip package available for your system, you may still be able to build it from source.

  4. How do you know which pytorch cuda version build to choose?

    It depends on the version of the installed NVIDIA driver. Here are the requirements for CUDA versions supported by pre-built pytorch releases:

    CUDA Toolkit NVIDIA (Linux x86_64)
    CUDA 10.0 >= 410.00
    CUDA 9.0 >= 384.81
    CUDA 8.0 >= 367.48

    So if your NVIDIA driver is less than 384, then you can only use CUDA 8.0. Of course, you can upgrade your drivers to more recent ones if your card supports it.

    You can find a complete table with all variations here.

    If you use NVIDIA driver 410+, you most likely want to install the cudatoolkit=10.0 pytorch variant, via:

    conda install -c pytorch pytorch cudatoolkit=10.0

    or if you need a lower version, use one of:

    conda install -c pytorch pytorch cudatoolkit=8.0
    conda install -c pytorch pytorch cudatoolkit=9.0

    For other options refer to the complete list of the available pytorch variants.


In order to update your environment, simply install fastai in exactly the same way you did the initial installation.

Top level files environment.yml and environment-cpu.yml belong to the old fastai (0.7). conda env update is no longer the way to update your fastai-1.x environment. These files remain because the fastai course-v2 video instructions rely on this setup. Eventually, once fastai course-v3 p1 and p2 will be completed, they will probably be moved to where they belong - under old/.

Contribution guidelines

If you want to contribute to fastai, be sure to review the contribution guidelines. This project adheres to fastai’s code of conduct. By participating, you are expected to uphold this code.

We use GitHub issues for tracking requests and bugs, so please see fastai forum for general questions and discussion.

The fastai project strives to abide by generally accepted best practices in open-source software development:


A detailed history of changes can be found here.

Copyright 2017 onwards, fast.ai, Inc. Licensed under the Apache License, Version 2.0 (the “License”); you may not use this project’s files except in compliance with the License. A copy of the License is provided in the LICENSE file in this repository.

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