async_property¶

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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.