friendly_ago_string.py

from datetime import datetime
import math

def friendly_ago_string(d):
    """
    Returns a friendly string like "8 minutes ago" representing the 
    differences between now and d.
    """
    if not d or not isinstance(d, datetime):
        return None
    
    ending = lambda diff: diff == 1 and " ago" or "s ago"
    rint   = lambda r, v: int(math.ceil(r)) if (r+1) % int(r+1) >= v\
                          else int(math.floor(r)) 

    dt = datetime.now().replace(tzinfo=None) - d.replace(tzinfo=None)
    days, seconds = dt.days, dt.seconds
    years, months, weeks, hours, mins = (rint(days/float(365), 0.6), 
                                         rint(days/float(30) , 0.85), 
                                         rint(days/float(7)  , 0.85), 
                                         rint(seconds/float(3600), 0.96),
                                         rint(seconds/float(60), 0.99))
    if years > 0:
        return str(years) + " year" + ending(years) 
    if months > 0:
        return str(months) + " month" + ending(months) 
    elif weeks > 0:
        return str(weeks) + " week" + ending(weeks)
    elif days > 0:
        return str(days) + " day" + ending(days)
    elif hours > 0:
        return str(hours) + " hour" + ending(hours)
    elif mins > 0:
        return str(mins) + " min" + ending(mins) 
    else:
        return str(seconds) + " sec" + ending(seconds)