Format a `timedelta` object to a string, such that only the significant portion is displayed.

timedelta_utils.py

def timedelta_format(td_object):
    '''                                                                            
    Format a timedelta object to a string such that only the significant           
    portion of it is displayed.                                                          
                                                                                   
    Some examples:                                                                 
                                                                                   
    12 days, 12:55:00  -> 12 days                                                  
    1 day, 12:00:00    -> 1 day                                                    
    1 day, 1:01:00     -> 1 day, 1 hour                                            
    1:00:00            -> 60 minutes                                               
    ''' 
    seconds = int(td_object.total_seconds())                                    
                                                                                
    PERIODS = [('year', 60*60*24*365), ('month', 60*60*24*30),                  
               ('day', 60*60*24), ('hour', 60*60), ('minute', 60),              
               ('second', 1)]                                                   
                                                                                
    strings = []                                                                
                                                                                
    found = False                                                               
    skipped = False                                                             
    last_period_value = 0                                                       
                                                                                
    for period_name, period_seconds in PERIODS:                                 
                                                                                
        if seconds > period_seconds:                                            
            if found and skipped:                                               
                break                                                           
                                                                                
            period_value, seconds = divmod(seconds, period_seconds)             
            if period_value == 1:                                               
                strings.append("%s %s" % (period_value, period_name))           
            else:                                                               
                if last_period_value > 2 and strings:                           
                    last_period_value = period_value                            
                    break                                                       
                strings.append("%s %ss" % (period_value, period_name))          
                if period_value > 1:                                            
                    last_period_value = period_value                            
                    break                                                       
                                                                                
            last_period_value = period_value                                    
            found = True                                                        
            skipped = False                                                     
        else:                                                                   
            skipped = True                                                      
                                                                                
    return " and ".join(strings[:2]) 

if __name__ == "__main__":                                                      
                                                                                   
    assert(timedelta_format(
        timedelta(days=12, hours=12, minutes=55)) == '12 days')       
    
    assert(timedelta_format(
        timedelta(days=1, hours=12)) == '1 day and 12 hours')         
    
    assert(timedelta_format(
        timedelta(days=1, hours=1, minutes=1)) == '1 day and 1 hour')
    
    assert(timedelta_format(
        timedelta(days=0, hours=1)) == '60 minutes')                  
    
    assert(timedelta_format(
        timedelta(days=0, hours=12)) == '12 hours')                   
    
    assert(timedelta_format(
        timedelta(days=0, hours=12, minutes=34)) == '12 hours')       
    
    assert(timedelta_format(
        timedelta(days=0, hours=1, seconds=6)) == '1 hour')           
    
    assert(timedelta_format(
        timedelta(days=0, hours=1, minutes=34)) == '1 hour and 34 minutes')
    
    assert(timedelta_format(
        timedelta(days=0, hours=0, minutes=1, seconds=12)) ==
        '1 minute and 12 seconds')