TypeError: unsupported operand type(s) for -: 'datetime.time' and 'datetime.time'

Question

my models.py:

class Attendancename(models.Model):
    teacher_name = models.ForeignKey(Teachername, default='Ram')
    date = models.DateField('Date', default=datetime.datetime.today)
    intime = models.TimeField('IN-TIME', auto_now=True)
    outtime = models.TimeField('OUT-TIME', auto_now=True)

    def hours_conversion(self):
        startdelta = datetime.timedelta(hours=self.intime.hours, minutes=self.intime.minutes, seconds=self.intime.seconds)
        enddelta = datetime.timedelta(hours=self.outtime.hours, minutes=self.outtime.minutes, seconds=self.outtime.seconds)
        return (enddelta-startdelta).seconds/3600

    def __str__(self):
        return "%s" %self.teacher_name

my views.py:

def add_atten(request):
    if request.method == 'POST':
        form = AttendancenameForm(request.POST)
        if form.is_valid():
            form.save()
            return HttpResponseRedirect(reverse('student:listatten'))
        else:
            print(form.errors)
    else:       
        form = AttendancenameForm()
    return render(request, 'add_atten.html', {'form': form},)

my forms.py:

class AttendancenameForm(ModelForm):
    intime = forms.TimeField(input_formats=('%H:%M',))
    outtime = forms.TimeField(input_formats=('%H:%M',))
    teacher_name = forms.ModelChoiceField(queryset=Teachername.objects.all())
    class Meta:
        model = Attendancename
        fields = ('teacher_name', 'date', 'intime', 'outtime',)

Actually I'm trying to calculate total number of hours based on difference of 'intime' and 'outtime' in my models.py file but it raises above erroe. I think I'm doing syntax error. Can anybody Please tell me what is the correct syntax or method to do so? Any body please suggest me what to do to fix it?

Answer 1

It's because you cannot subtract a datetime.time from a datetime.time. Convert them to datetime.datetime objects and it'll return a datetime.timedelta object that you could use.

If you're lucky enough to be using Django 1.8, they now have a DurationField that can be used.

Failing that, I would recommend converting the timedelta into either seconds or a floating point representation so you can actually store it to the database.

EDIT: Pulled up in comments for half arsing an answer.

For example - if you want to store the number of (integer) seconds, you can convert from a TimeDelta by using secs = td // timedelta(seconds=1).