Source code for paco.reduce

# -*- coding: utf-8 -*-
import asyncio
from .decorator import overload
from .concurrent import ConcurrentExecutor
from .assertions import assert_corofunction, assert_iter

[docs]@overload @asyncio.coroutine def reduce(coro, iterable, initializer=None, limit=1, right=False, loop=None): """ Apply function of two arguments cumulatively to the items of sequence, from left to right, so as to reduce the sequence to a single value. Reduction will be executed sequentially without concurrency, so passed values would be in order. This function is the asynchronous coroutine equivalent to Python standard `functools.reduce()` function. This function is a coroutine. This function can be composed in a pipeline chain with ``|`` operator. Arguments: coro (coroutine function): reducer coroutine binary function. iterable (iterable|asynchronousiterable): an iterable collection yielding coroutines functions. initializer (mixed): initial accumulator value used in the first reduction call. limit (int): max iteration concurrency limit. Use ``0`` for no limit. right (bool): reduce iterable from right to left. loop (asyncio.BaseEventLoop): optional event loop to use. Raises: TypeError: if input arguments are not valid. Returns: mixed: accumulated final reduced value. Usage:: async def reducer(acc, num): return acc + num await paco.reduce(reducer, [1, 2, 3, 4, 5], initializer=0) # => 15 """ assert_corofunction(coro=coro) assert_iter(iterable=iterable) # Reduced accumulator value acc = initializer # If interable is empty, just return the initializer value if len(iterable) == 0: return initializer # Create concurrent executor pool = ConcurrentExecutor(limit=limit, loop=loop) # Reducer partial function for deferred coroutine execution def reducer(element): @asyncio.coroutine def wrapper(): nonlocal acc acc = yield from coro(acc, element) return wrapper # Support right reduction if right: iterable.reverse() # Iterate and attach coroutine for defer scheduling for element in iterable: pool.add(reducer(element)) # Wait until all coroutines finish yield from # Returns final reduced value return acc