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Fastai FAQs for Beginners

Q1: How to ask for help for fastai

use this code - notice the 3 ` enclosing the code block:

triple_backticks

to render this:

~/.conda/envs/tf-gpu/lib/python3.6/multiprocessing/popen_fork.py in __init__(self, process_obj)
     18         sys.stderr.flush()
     19         self.returncode = None
---> 20         self._launch(process_obj)
     21 
     22     def duplicate_for_child(self, fd):

~/.conda/envs/tf-gpu/lib/python3.6/multiprocessing/popen_fork.py in _launch(self, process_obj)
     65         code = 1
     66         parent_r, child_w = os.pipe()
---> 67         self.pid = os.fork()
     68         if self.pid == 0:
     69             try:

OSError: [Errno 12] Cannot allocate memory

Q2: Where can I put my Jupter Notebook?

🔴 NOTE: Do NOT put your Jupyter Notebook under the /data/ directory! Here's the link for why.

Option 1 (default): under /courses

The default location is under the dl1 folder, wherever you've cloned the repo on your GPU machine.

my example

(fastai) paperspace@psgyqmt1m:~$ ls
anaconda3  data  downloads  fastai
  • Paperspace: /home/paperspace/fastai/courses/dl1
  • AWS: /home/ubuntu/fastai/courses/dl1

Option 2: where you want

If you change the default location of your notebook, you'll need to update your .bashrc file. Add in the path to where you've cloned the fastai GitHub repo:

  • for me, my notebooks are in a "projects" directory: ~/projects
  • my fastai repo is cloned at the root level, so it is here: ~/fastai

in the file .bashrc add this path:

export PYTHONPATH=$PYTHONPATH:~/fastai

Reminder: don't forget to run (or source) your .bashrc file:

  1. add path where fastai repo is to .bashrc
  2. save and exit
  3. source it: source ~/.bashrc

Option 3: used pip install

Note that if you did pip install, you don't need to specify the path (as in option 2, or you don't need to put in the courses folder, as in option 1).
However, fastai is still being updated so there is a delay in library being available directly via pip.
Can try:
pip install https://github.com/fastai/fastai/archive/master.zip

Q3: What does my directory structure look like?

my path

PATH = "/home/ubuntu/data/dogscats/"

looking at my directory structure

!tree {PATH} -d
/home/ubuntu/data/dogscats/
├── models
├── sample
│   ├── models
│   ├── tmp
│   ├── train
│   │   ├── cats
│   │   └── dogs
│   └── valid
│       ├── cats
│       └── dogs
├── test
├── train
│   ├── cats
│   └── dogs
└── valid
    ├── cats
    └── dogs

Notes on directories

  • models directory: created automatically
  • sample directory: you create this with a small sub-sample, for testing code
  • test directory: put any test data there if you have it
  • train/test directory: you create these and separate the data using your own data sample
  • tmp directory: if you have this, it was automatically created after running models
  • fastai / keras code automatically picks up the label of your categories based on your folders. Hence, in this example, the two labels are: dogs, cats

Notes on image file names

  • not important, you can name them whatever you want

Getting file counts

looking at file counts

# print number of files in each folder

print("training data: cats")
!ls -l {PATH}train/cats | grep ^[^dt] | wc -l

print("training data: dogs")
!ls -l {PATH}train/dogs | grep ^[^dt] | wc -l

print("validation data: cats")
!ls -l {PATH}valid/cats | grep ^[^dt] | wc -l

print("validation data: dogs")
!ls -l {PATH}valid/dogs | grep ^[^dt] | wc -l

print("test data")
!ls -l {PATH}test1 | grep ^[^dt] | wc -l

my output

training data: cats
11501
training data: dogs
11501
validation data: cats
1001
validation data: dogs
1001
test data
12501

Q4: What is a good train/validation/test split?

  • can do 80/20 (train/validation)
  • if you have or are creating a 'test' split, use for (train/validation/test):
    • can do 80/15/5
    • can do 70/20/10
    • can do 60/20/20

Note: Depending on who the instructor is, they use various naming conventions:

  • train/test and then validation for holdout data
  • train/validation and then test for holdout data

It's important to understand that:

  • in the case of train/test, the test set is used to test for generalization
  • the holdout data is a second test set

Q5: How do I copy files or data from my local computer to a cloud machine (Paperspace, AWS, etc)?

Instructions on using scp command to transfer files from platforms

Q6: Where do I put my sample images?

testing sample images after the model has been created