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Description:

asyncpromises 1.1.1

Promise
This is a implementation of Promises in Python. It is a super set of
Promises/A+ designed to have readable, performant code and to provide
just the extensions that are absolutely necessary for using async_promises in
Python.
This was forked to make it fully compatible with the Promise/A+
spec
On completion of promise PR #20,
maintenence for this fork will be dropped.

Installation
$ pip install async_promises

Usage
The example below shows how you can load the async_promises library. It then
demonstrates creating a async_promises from scratch. You simply call
Promise(fn). There is a complete specification for what is returned
by this method in
Promise/A+.
from async_promises import Promise

async_promises = Promise(
lambda resolve, reject: resolve('RESOLVED!')
)

API
Before all examples, you will need:
from async_promises import Promise

Promise(resolver)
This creates and returns a new Promise. resolver must be a function.
The resolver function is passed two arguments:

resolve should be called with a single argument. If it is called
with a non-promise value then the promise is fulfilled with that
value. If it is called with a promise (A) then the returned promise
takes on the state of that new promise (A).
reject should be called with a single argument. The returned
promise will be rejected with that argument.

Class Methods
These methods are invoked by calling Promise.methodName.

Promise.resolve(value)
Converts values and foreign Promises into Promise/A+ Promises. If you
pass it a value then it returns a Promise for that value. If you pass it
something that is close to a promise (such as a jQuery attempt at a
promise) it returns a Promise that takes on the state of value
(rejected or fulfilled).

Promise.rejected(value)
Returns a rejected promise with the given value.

Promise.all(list)
Returns a Promise for a list. If it is called with a single argument
then this returns a Promise for a copy of that list with any Promises
replaced by their fulfilled values. e.g.
p = Promise.all([Promise.resolve('a'), 'b', Promise.resolve('c')]) \
.then(lambda res: res == ['a', 'b', 'c'])

assert p.get() is True

Promise.promisify(obj)
This function wraps the obj act as a Promise if possible. Python
Futures are supported, with a callback to async_promises.done when
resolved.

Promise.for_dict(d)
A special function that takes a dictionary of Promises and turns them
into a Promises for a dictionary of values. In other words, this turns an
dictionary of Promises for values into a Promises for a dictionary of
values.

Instance Methods
These methods are invoked on a Promise instance by calling
myPromise.methodName

async_promises.then(on_fulfilled, on_rejected)
This method follows the Promise/A+
spec. It explains
things very clearly so I recommend you read it.
Either on_fulfilled or on_rejected will be called and they will
not be called more than once. They will be passed a single argument and
will always be called asynchronously (in the next turn of the event
loop).
If the Promise is fulfilled then on_fulfilled is called. If the
Promise is rejected then on_rejected is called.
The call to .then also returns a Promise. If the handler that is
called returns a Promise, the Promise returned by .then takes on the
state of that returned Promise. If the handler that is called returns a
value that is not a Promise, the Promise returned by .then will be
fulfilled with that value. If the handler that is called throws an
exception then the Promise returned by .then is rejected with that
exception.

async_promises.catch(on_rejected)
Sugar for async_promises.then(None, on_rejected), to mirror catch in
synchronous code.

async_promises.done(on_fulfilled, on_rejected)
The same semantics as .then except that it does not return a Promise
and any exceptions are re-thrown so that they can be logged (crashing
the application in non-browser environments)

Other package functions
is_thenable(obj)
This function checks if the obj is a Promise, or could be
promisifyed.

Notes
This package is heavily insipired in
aplus.

License
MIT
License