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Python decorator for async properties.

Project description

async_property

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Python decorator for async properties.

Install

To install async_property, run this command in your terminal:

$ pip install async-property

Or if you have pipenv:

$ pipenv install 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):
        return 'works every time'

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

Features

  • Both regular and cached property.
  • @async_cached_property can be accessed multiple times without repeating function call.
  • @async_cached_property uses asyncio.Lock to ensure function is called only once per instance.
  • 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.

History

0.2.1 (2019-04-13)

  • Update docs and readme

0.2.0 (2019-04-12)

  • Use instance state to hold cache and locks

0.1.4 (2019-04-12)

  • Fix inheritance issues on AwaitLoader

0.1.3 (2019-04-12)

  • Cleanup code

0.1.2 (2019-04-12)

  • Fix asyncio.Lock issues

0.1.1 (2019-04-11)

  • Complete test coverage and update readme

0.1.0 (2019-04-11)

  • First release on PyPI.

Project details


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