DateTime object is none -- Python

Question

I'm doing this inside Django. The DateTime string is passed into POST successfully. This is my code:

vk = Vk()
day1 = request.POST['day1']
vk.day1 = datetime.datetime.strptime(day1, '%m/%d/%Y %I:%M %p')
vk.save()

This is the format of the POST info:

'day1': 'MM/DD/YYYY HH:MM AM/PM' # AM/PM meaning either AM or PM

The problem is that the DateTimeField on the vk instance is None.

class Vk(models.Model):
    day1 = models.DateTimeField(null=True, blank=True)

I see that it is None in my HTML file:

{% for vk in vk %}
{{ vk.day1 }}
{% endfor %}

which amounts to None.

This is the view that is responsible for rendering the template:

def list_verkefni(request):
    vk = Vk.objects.all()
    vm = Vm.objects.all()

    return render(request, 'list_verkefni.html', 
    {'vk': vk, 'vm': vm}
    )

Thanks. How do you check that the value of day1 is saved as None? — alecxe
– alecxe, Commented Aug 8, 2014 at 13:21
Updated the OP again. I have faith in the template, but I'll check the console just in case — Firkamon
– Firkamon, Commented Aug 8, 2014 at 13:25
Good, then what is Vk variable passed to the template? Could you show the view which is responsible for rendering the template? — alecxe
– alecxe, Commented Aug 8, 2014 at 13:27
Updated, but I can confirm that the view is working correctly because it is displaying other attributes (unrelated) of Vk correctly — Firkamon
– Firkamon, Commented Aug 8, 2014 at 13:31

Bruce · Accepted Answer · 2014-08-08 15:08:43Z

Why don't you use ModelForm?

someapp/forms.py:

class VkForm(forms.ModelForm):
    class Meta:
        model = Vk
        fields = ('day1', )

    def __init__(self, *args, **kwargs):
        super(VkForm, self).__init__(*args, **kwargs)
        self.fields['day1'].input_formats = ['%m/%d/%Y %I:%M %p', ]

someapp/views.py:

def myview(request):
    form = VkForm(request.POST or None)
    if request.method == "POST" and form.is_valid():
        obj = form.save()
        return HttpResponseRedirect('/somewhere/')
    return render(
        request, 'template.html',
        {'form': form}
    )

Yes, you write a little bit more code, but:

you get full validation with nice error messages
whenever you extend your model in future, you don't need to rewrite the code, just add the field name into ModelForm
you don't need to do low level conversion to Python data types

This is considered a bad practise:

{% for vk in vk %}
{{ vk.day1 }}
{% endfor %}

Although this works in Django template engine, it is very confusing. If you would write the same in Python, vk will be overwritten. Whenever you work with a list of items, append _list to the variable name, e.g.: object_list or vk_list to distinguish between a single object and a list.

To better debug a code, I would suggest to pip install pudb and do something like this:

vk = Vk()
day1 = request.POST['day1']
import pudb; pudb.set_trace()
vk.day1 = datetime.datetime.strptime(day1, '%m/%d/%Y %I:%M %p')
vk.save()

Run the local dev server, do the POST request and check your terminal. Check if request.POST['day1'] is really what you expect to be and if it the datetime instance was set on your day atribute.

Thanks, this would have saved me a lot of headache I think. I'll do this.

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