Python [fire](https://github.com/google/python-fire) is extremely useful for automatically generating command line interfaces (CLIs) from absolutely any Python object.

Examples: 

The python class:
```python
import fire

class Calculator(object):
  """A simple calculator class."""

  def double(self, number):
    return 2 * number

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

Then, when calling the file on the terminal, the CLI is already there: 
```shell
python calculator.py double 10  # 20
python calculator.py double --number=15  # 30
```