Inpromptu

A library for inferring interactive prompts from object instances.

What Inpromptu Is

Inpromptu is a near-direct replacement for Python's built-in cmd.py utility. Rather than rewrite an extra class with special do_ methods, Inpromptu will infer a prompt from the class directly. Inpromptu takes an object instance's callables and exposes them in a read-evaluate-print-loop that supports tab-completion.

Born from a need to quickly interact with real-world devices and a frustration from the manual overhead of cmd.py, Inpromptu automatically generates an interactive prompt session by taking advantage of Python's type hinting and introspection capabilities. Features include

• seamless automatic tab completion using a method's function signature
  • supports: bool, int, float, str, anything that inherits from Enum
• automatic help generation using a method's docstring

Inpromptu also provides a prompt_toolkit-compatible completer so you can build more complicated prompts while getting all of inpromptu's introspection elements for free.

What Inpromptu Isn't

Inpromptu creates an interactive prompt. Inpromptu is not:

• a command line interface generator. See argparse, python-fire, or click for that.
• a api-replacement for cmd.py. There are some differences, mainly the lack of do_ methods. Have a go at the examples.

Requirements

• Python 3.6 or later
• all methods that will support completion must have all parameters type-hinted

Installation

You can install this latest stable version of this package from PyPI with

pip install inpromptu

Or you can clone this repository and, from within this directory, install inpromptu in editable mode with

pip install -e .

Example Time

Start with a class in file such as test_drive.py.

class TestDrive:

    def __init__(self):
        """initialization!"""
        self.vehicle_speed = 0

    honk(self):
        """beep the horn."""
        print("Beep!")

    speed(self):
        """return the vehicle speed."""
        return self.vehicle_speed

Create a prompt with Inpromptu.

from inpromptu import Inpromptu

my_test_drive = TestDrive()
my_prompt = Inpromptu(my_test_drive)
my_prompt.cmdloop()

Run it!

python3 test_drive.py

This should produce a prompt:

>>>

Press tab twice to show all your callable attributes.

honk            speed
>>>

Great! Now let's demo argument completion.

First, add a function with type-hinted annotations for all input arguments (except self or cls).

add_fuel(self, gallons: float = 0, top_off: bool = False):
    """Add fuel in gallons.""
    pass

Run it!

python3 test_drive.py

Start typing at the prompt

>>> add_f

Press tab to complete any function.

>>> add_fuel

Put a space between the command and press tab twice.

gallons=<float> top_off=<False>
>>> add_fuel 

Magic! At this point you can finish entering the command in many ways.

>>> add_fuel gallons=10 top_off=False

OR

>>> add_fuel 10 False

OR

>>> add_fuel 10 top_off=False

In other words, arguments can be filled out by name or by position or by a combination of position first, then by name--just like how *args and **kwds behave on normal python functions.

So what are you waiting for? Why not take it for a test drive? From the example directory, run:

python3 test_drive.py

FAQs

Why not just use the python shell?

You could! Inpromptu is intented to be a bit more minimalistic and user-friendly. Inpromptu can be used as a minimalistic UI on its own.

Is there any way I can tease out the core elements to build my own interface?

Yes. In fact, core elements of Inpromptu can be hooked directly into Python Prompt Toolkit to provide the same kind of object-based completions with richer prompt features. See the examples folder for some inspiration.

What's not implemented?

• functions that use *args and **kwargs as input
• The @overload operator.
• input arguments that can be various types (i.e: Union[int, str, float]).
• functions wrapped in decorators: like @cache, @cached_property from functools
  • Note: some cases may work already.

What's Going to be Implemented Next?

• Bare Minimum Union type implementation:
  • Unions where None is one of the options Union[None, int]
• Explicit handling of functions wrapped in decorators.

About the Author

Inpromptu was written by someone who used cmd.py one-too-many times. There had to be a better solution. And Inpromptu is one of many.