Using the Python Fire Library to Build Simple Command-Line Interfaces

Why Use Fire

When building command-line tools in Python, the built‑in argparse module can become verbose and unwieldy, while click adds complexity for larger scripts. The fire library generates CLIs automatically with just two lines of code, making it faster and more readable.

Installation

# pip
pip3 install fire

# conda
conda install fire -c conda-forge

# source
python3 setup.py install

Basic Usage

Expose a function as a CLI:

import fire

def hello(name):
    return 'Hello {name}!'.format(name=name)

if __name__ == '__main__':
    fire.Fire()

Run with:

$ python example.py hello World
Hello World!

Expose a specific function:

import fire

def hello(name):
    return 'Hello {name}!'.format(name=name)

if __name__ == '__main__':
    fire.Fire(hello)

Run with:

$ python example.py World
Hello World!

Multiple Commands

Bind all functions automatically:

import fire

def add(x, y):
    return x + y

def multiply(x, y):
    return x * y

if __name__ == '__main__':
    fire.Fire()

Or provide a dictionary for custom command names:

import fire

def add(x, y):
    return x + y

def multiply(x, y):
    return x * y

if __name__ == '__main__':
    fire.Fire({'add': add, 'multiply': multiply})

Advanced Features

Command grouping with classes:

class IngestionStage(object):
    def run(self):
        return 'Ingesting! Nom nom nom...'

class DigestionStage(object):
    def run(self, volume=1):
        return ' '.join(['Burp!'] * volume)
    def status(self):
        return 'Satiated.'

class Pipeline(object):
    def __init__(self):
        self.ingestion = IngestionStage()
        self.digestion = DigestionStage()
    def run(self):
        self.ingestion.run()
        self.digestion.run()
        return 'Pipeline complete'

if __name__ == '__main__':
    fire.Fire(Pipeline)

Accessing attributes directly:

class Airport(object):
    def __init__(self, code):
        self.code = code
        self.name = dict(airports).get(self.code)
        self.city = self.name.split(',')[0] if self.name else None

if __name__ == '__main__':
    fire.Fire(Airport)

Custom callbacks and argument parsing are also supported, allowing automatic type inference and flexible separators.