update-latest.py

from distutils.version import StrictVersion
from urllib.request import urlopen
import json
from collections import OrderedDict

# Get list of versions from pypi
pypi = json.loads(urlopen('https://pypi.python.org/pypi/wagtail/json').read().decode('utf-8'))
versions = [StrictVersion(v) for v in pypi['releases'].keys()]

# Filter out prereleases (betas, alphas, etc)
versions = filter(lambda v: not v.prerelease, versions)

# Get highest version
highest_version = str(sorted(versions)[-1])

# Get url to release notes
release_notes_url = 'http://docs.wagtail.io/en/v{version}/releases/{version}.html'.format(version=highest_version)

# Create latest.txt file
with open('latest.txt', 'w') as f:
    f.write(json.dumps(OrderedDict([
        ('version', highest_version),
        ('url', release_notes_url),
    ]), indent=4))