From 45b55e23d34371986ee0da5be784a1f2134fd58a Mon Sep 17 00:00:00 2001 From: Adrian Tschira Date: Sun, 29 Apr 2018 13:54:38 +0200 Subject: [PATCH] Add batch_iter to utils There's a frequent idiom I noticed where an iterable is split up into a number of chunks/batches. Unfortunately that method does not work with iterators like dict.keys() in python3. This implementation works with iterators. Signed-off-by: Adrian Tschira --- synapse/util/__init__.py | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/synapse/util/__init__.py b/synapse/util/__init__.py index 814a7bf71b..fc11e26623 100644 --- a/synapse/util/__init__.py +++ b/synapse/util/__init__.py @@ -20,6 +20,8 @@ from twisted.internet import defer, reactor, task import time import logging +from itertools import islice + logger = logging.getLogger(__name__) @@ -79,3 +81,19 @@ class Clock(object): except Exception: if not ignore_errs: raise + + +def batch_iter(iterable, size): + """batch an iterable up into tuples with a maximum size + + Args: + iterable (iterable): the iterable to slice + size (int): the maximum batch size + + Returns: + an iterator over the chunks + """ + # make sure we can deal with iterables like lists too + sourceiter = iter(iterable) + # call islice until it returns an empty tuple + return iter(lambda: tuple(islice(sourceiter, size)), ())