Skip to main content
This is a pre-production deployment of Warehouse. Changes made here affect the production instance of PyPI (
Help us improve Python packaging - Donate today!

Provides a utility for constructing generators out of an iterable that yield look-ahead (and/or “look-behind”) tuples.

Project Description

Constructs a generator over the iterable yielding look-ahead (and/or “look-behind”) tuples. One tuple will be generated for each element value accessible from the iterator, containing that element and the number of elements specified just prior to and immediately after. When no such element exists, the None is used instead.

If one were to think of iterator as a list, this is would be similar to appending [None]*lookahead and prepending [None]*lookbehind, then iterating over and returning a sliding window of length lookbehind+1+ lookahead (except of course that instead of generating the such a list, this implementation generates (and caches) lookahead values only as needed).

lookahead() may be called with 1, 2, or 3 parameters:

Defaults to lookahead=1, lookbehind=0
lookahead(iterable, lookahead)
Defaults to lookbehind=0
lookahead(iterable, lookbehind, lookahead)
Notice that lookahead is now the 3rd parameter!

Example semantics:

yield (item, next)
lookahead(iterable, 2):
yield (item, next, next+1)
lookahead(iterable, 1, 2):
yield (prev, item, next, next+1)
lookahead(iterable, p, n):
yeild (prev, …, prev+p-1, item, next, …, next+n-1)

Release History

This version
History Node


Download Files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Filename, Size & Hash SHA256 Hash Help File Type Python Version Upload Date
(2.4 kB) Copy SHA256 Hash SHA256
Source None Sep 12, 2013

Supported By

Elastic Elastic Search Pingdom Pingdom Monitoring Dyn Dyn DNS Sentry Sentry Error Logging CloudAMQP CloudAMQP RabbitMQ Heroku Heroku PaaS Kabu Creative Kabu Creative UX & Design Fastly Fastly CDN DigiCert DigiCert EV Certificate Google Google Cloud Servers