resumeback 0.1.0

Library for using callbacks to resume your code.

A Python library for using callbacks to resume your code.

resumeback provides a utility function decorator that enables using callback-based interfaces in a single line of execution – a single function.

Full docs are available here: http://fichtefoll.github.io/resumeback/

Installation

$ pip install resumeback

Usage

resumeback.send_self’s mechanic of sending a generator function a handle to itself is what allows for better flow control using callback-based interfaces. Essentially, it enables a single line of execution.

Following is a function that uses an asynchronous callback mechanism to signal that user input has been made:

from threading import Thread

def ask_for_user_input(question, on_done):
    def watcher():
        result = input(question)
        on_done(result)

    Thread(target=watcher).start()

The traditional way of using a function like ask_for_user_input would be to define a function of some way, either as a closure or using functools.partial so that we can preserve the state we already accumulated prior to executing said function.

For example like so:

def main():
    arbitrary_value = 10

    def on_done(number):
        number = str(number)
        print("Result:", number * arbitrary_value)

    ask_for_user_input("Please enter a number", on_done)

Because Python does not have multi-line inline functions, this is rather awkward, because we are jumping from the function call of ask_for_user_input back to our previously defined function on_done – which is only ever going to be called once in this context.

However, using resumeback.send_self, we can do something to flatten our line of execution by passing a callback to resume execution in our original function:

from resumeback import send_self

@send_self
def main():
    this = yield  # "this" is now a reference to the just-created generator
    arbitrary_value = 10

    # Yield pauses execution until one of the generator methods is called,
    # such as `.send`, which we provide as the callback parameter.
    number = yield ask_for_user_input("Please enter a number", this.send)
    number = str(number)
    print("Result:", number * arbitrary_value)

Acknowledgements

Project started initially after a forum post from @Varriount on the Sublime Text forum. I just took his idea “to the next (abstraction) level” and made it more convenient to use.