async_property

Python decorator for async properties.

• Python: 3.7+
• Free software: MIT license
• Documentation: https://async-property.readthedocs.io
• Package: https://pypi.org/project/async-property
• Source code: https://github.com/ryananguiano/async_property

Install

To install async_property, run this command in your terminal:

$ pip install async-property

Or if you have pipenv:

$ pipenv install async-property

Or alternatively with conda:

$ conda install -c ryananguiano async-property

Usage

You can use @async_property just as you would with @property, but on an async function.

class Foo:
    @async_property
    async def remote_value(self):
        return await get_remote_value()

The property remote_value now returns an awaitable coroutine.

instance = Foo()
await instance.remote_value

Cached Properties

@async_cached_property will call the function only once. Subsequent awaits to the property will return a cached value.

class Foo:
    @async_cached_property
    async def value(self):
        print('loading value')
        return 123

>>> instance = Foo()
>>> instance.value
<AwaitableOnly "Foo.value">

>>> await instance.value
loading value
123
>>> await instance.value
123
>>> instance.value
123

>>> instance.value = 'abc'
>>> instance.value
'abc'
>>> await instance.value
'abc'

>>> del instance.value
>>> await instance.value
loading value
123

AwaitLoader

If you have an object with multiple cached properties, you can subclass AwaitLoader. This will make your class instances awaitable and will load all @async_cached_property fields concurrently. AwaitLoader will call await instance.load(), if it exists, before loading properties.

class Foo(AwaitLoader):
    async def load(self):
        print('load called')

    @async_cached_property
    async def db_lookup(self):
        return 'success'

    @async_cached_property
    async def api_call(self):
        print('calling api')
        return 'works every time'

>>> instance = await Foo()
load called
calling api
>>> instance.db_lookup
'success'
>>> instance.api_call
'works every time'

Features

• Both regular and cached property.
• Cached properties can be accessed multiple times without repeating function call.
• Uses asyncio.Lock to ensure cached functions are called only once.
• Full test coverage with py.test

Credits

This package was created with Cookiecutter and the audreyr/cookiecutter-pypackage project template.

The ObjectProxy class was taken from wrapt library by Graham Dumpleton.