Creating Scripts

Notebooks are great for exploration. And with NBDev they’re pretty amazing for development work too! But sometimes you just want a nice command-line script so that you can run your code with some thing like:

python my_script.py --input cat.png --width 128 

In this quick notebook I’ll show you my new favourite way of doing this, using fastcore.script. The example from their docs shows how simple this can be. We write the following to a file:

from fastcore.script import *
@call_parse
def main(msg:str,     # The message
         upper:bool): # Convert to uppercase?
    "Print `msg`, optionally converting to uppercase"
    print(msg.upper() if upper else msg)

Overwriting scripts/example_script.py

Now we can run this like so:

!python scripts/example_script.py --upper 'Hello World'

HELLO WORLD

And those type hints and comments in the function definition above? They become part of the help text:

!python scripts/example_script.py -h

usage: example_script.py [-h] [--upper] msg

Print `msg`, optionally converting to uppercase

positional arguments:
  msg         The message

options:
  -h, --help  show this help message and exit
  --upper     Convert to uppercase? (default: False)

Pretty nifty right!

Check out the scripts/ directory for a bunch of examples which I made using this technique to go along with the course.