pasync's Introduction

pasync - A simple event loop for async python

This minimal package is mainly used to explore implementing an async runtime in Python.

Installation

pip install pasync

Usage

Runner

The main construct that you'll often work with is Runner.

A runner is actually a wrapper around an event loop.

It comes with two flavors: non-blocking runner and blocking runner.

A blocking runner will run all the tasks till end, blocking the main thread. When given a set of tasks, it will refuse to accept any task in the meaning time.
A non-blocking runner will run all the tasks in another thread. Unlike a blocking runenr, it can accepts additional tasks in the meaning time.

By default, a runner is blocking.

Blocking runner

async def gen_num(n):
  return n

with Runner() as runner:
  assert runner.run_task(gen_num(1)) == 1
  assert runner.gather(gen_num(1), gen_num(2)) == [1, 2]

Non-blocking runner

async def gen_num(n):
  return n

with Runner(non_blocking = True) as runner:
  assert runner.run_task(gen_num(1)) == None             # Not support returning results yet
  assert runner.gather(gen_num(1), gen_num(2)) == None   # Not support returning results yet

Promise

Promise is intended to simulate Promise in js. Its usage and semantics should be the same.

Promise itself is an awaitable, so it can be passed to Runner.run_task

Promise.then and Promise.catch return another promise.

Pitfalls

Currently, non-blocking runner cannot return results of tasks yet. This can be worked around by making the top-level task return None, while all the subtasks's results are consumed inside the top-level task

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