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Python Fire

Developer UtilitiesCLI/UtilsPython
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What it is

Python Fire is a library for automatically generating command-line interfaces (CLIs) from any Python object, such as functions, classes, or dictionaries. It enables rapid CLI creation without boilerplate code.

Python Fire generates a CLI automatically from Python code. It parses command-line arguments and maps them to function parameters, class methods, or dictionary keys. It supports nested objects and provides help and error messages automatically.

Installation

pip install fire

Getting started

The smallest useful thing you can do with it, and what each part means.

Creating a CLI from a function
import fire

def greet(name='World'):
    return f'Hello, {name}!'

if __name__ == '__main__':
    fire.Fire(greet)
Generates a command-line interface where you can run `python script.py --name Alice` to print `Hello, Alice!`.
Creating a CLI from a class
import fire

class Calculator:
    def add(self, x, y):
        return x + y

if __name__ == '__main__':
    fire.Fire(Calculator)
Generates a CLI from the `Calculator` class. You can run `python script.py add 3 5` to get `8`.

Advanced usage

Where the library earns its place over a simpler alternative.

Nested commands
import fire

class Math:
    class Operations:
        @staticmethod
        def multiply(x, y):
            return x * y

if __name__ == '__main__':
    fire.Fire(Math)
Supports nested objects. You can run `python script.py Operations multiply 3 4` to get `12`.
Using dictionaries
import fire

config = {
    'host': 'localhost',
    'port': 8080
}

if __name__ == '__main__':
    fire.Fire(config)
Exposes a dictionary as a CLI. Running `python script.py host` prints `localhost`.
Customizing CLI behavior
import fire

class App:
    def run(self, debug=False):
        print(f'Running app with debug={debug}')

if __name__ == '__main__':
    fire.Fire(App)
Supports flags and optional arguments. Running `python script.py run --debug True` enables debug mode.

Errors and fixes

The failures you are most likely to hit, and what actually resolves them.

TypeError: Missing required positional argument
Ensure that all required function parameters are provided in the CLI call.
FireError: Unsupported type
Python Fire may not handle certain types; convert objects to standard Python types (str, int, float, list, dict) before exposing.

Best practices

  • Use Python Fire for quick CLI tools without manually parsing arguments.
  • Avoid exposing sensitive functions or credentials via Fire CLIs.
  • Keep CLI entry points simple and delegate complex logic to underlying functions or classes.
  • Use docstrings to provide helpful documentation for automatically generated CLI help.
  • Combine Fire with logging or exception handling for robust command-line tools.

Background

Why it exists, and what it was reacting to.

Python Fire was created by Google in 2017 to make it easy to turn existing Python code into CLI tools. It allows developers to quickly expose functionality without writing repetitive argument parsing code, making it popular for scripting, automation, and testing.

Related libraries

Others in Developer Utilities for Python.

← All Python librariesPython guide