filters.py

from datetime import datetime
import jinja2
import flask

blueprint = flask.Blueprint('filters', __name__)

@jinja2.contextfilter
@blueprint.app_template_filter("split_hyphen")
def split_hyphen(context, string):
    return string.replace("-", " ")

# http://flask.pocoo.org/snippets/33/
# and
# http://stackoverflow.com/questions/12288454/how-to-import-custom-jinja2-filters-from-another-file-and-using-flask
@jinja2.contextfilter
@blueprint.app_template_filter("timesince")
def friendly_time(context, dt, past_="ago",
    future_="from now",
    default="just now"):
    """
    Returns string representing "time since"
    or "time until" e.g.
    3 days ago, 5 hours from now etc.
    """

    now = datetime.utcnow()
    try:
        trimmed_time = dt[:19]
        dt = datetime.strptime(trimmed_time, "%Y-%m-%d %H:%M:%S")
    except:
        pass
    try:
        # Thu, 26 Feb 2015 03:45:21 GMT
        dt = datetime.strptime(dt, "%a, %d %b %Y %H:%M:%S %Z")
    except:
        pass

    if now > dt:
        diff = now - dt
        dt_is_past = True
    else:
        diff = dt - now
        dt_is_past = False

    periods = (
        (diff.days / 365, "year", "years"),
        (diff.days / 30, "month", "months"),
        (diff.days / 7, "week", "weeks"),
        (diff.days, "day", "days"),
        (diff.seconds / 3600, "hour", "hours"),
        (diff.seconds / 60, "minute", "minutes"),
        (diff.seconds, "second", "seconds"),
    )

    for period, singular, plural in periods:

        if period:
            return "%d %s %s" % (period, \
                singular if period == 1 else plural, \
                past_ if dt_is_past else future_)

    return default