Django DurationField

duration.py

from django import forms
from django.db import models

def split_duration(value):
    if value:
        return ( '%02d' % (value // 3600), 
                 '%02d' % ((value % 3600) // 60), 
                 '%02d' % (value % 60),
                  )
    return ('00', '00', '00')

class DurationWidget(forms.widgets.MultiWidget):
    def __init__(self, attrs=None):
        defaults = {'style': 'width: 2em'}
        if attrs:
            defaults.update(attrs)
        widgets = [ forms.TextInput(attrs=defaults) ] * 3
        super(DurationWidget, self).__init__(widgets, defaults)

    def decompress(self, value):
        return split_duration(value)

    def format_output(self, rendered_widgets):
        return u' : '.join(rendered_widgets)

class DurationFormField(forms.MultiValueField):
    widget = DurationWidget

    def __init__(self, fields=None, *args, **kwargs):
        fields = [ forms.IntegerField(min_value=0, max_value=59) ] * 3
        super(DurationFormField, self).__init__(fields, *args, **kwargs)

    def compress(self, data_list):
        if not data_list:
            return None
        duration = 0
        for i, value in enumerate(data_list):
            if value in forms.fields.EMPTY_VALUES:
                continue
            duration += value * (60 ** (2-i))
        return duration

class Duration(int):
    def __unicode__(self):
        return ':'.join(split_duration(self))
        
class DurationField(models.Field):
    __metaclass__ = models.SubfieldBase
    
    def db_type(self):
        return 'int'
        
    def formfield(self, **kwargs):
        defaults = {'form_class': DurationFormField}
        defaults.update(kwargs)
        return super(DurationField, self).formfield(**defaults)        

    def to_python(self, value):
        if isinstance(value, Duration):
            return value
        try:
            return Duration(value)
        except ValueError:
            return value