Python – Django Model returning NoneType

djangodjango-viewspython

I have a model Product

it has two fields size & colours among others

colours = models.CharField(blank=True, null=True, max_length=500)
size = models.CharField(blank=True, null=True, max_length=500)

In my view I have

current_product = Product.objects.get(slug=title)
if len(current_product.size) != 0 :
    current_product.size = current_product.size.split(",")

and get this error:

object of type 'NoneType' has no len()

What is NoneType and how can I test for it?

Best Solution

NoneType is the type that the None value has. You want to change the second snippet to

if current_product.size: # This will evaluate as false if size is None or len(size) == 0.
  blah blah

Related Solutions

Python – django – inlineformset_factory with more than one ForeignKey

If I understand you correctly:

To change what is displayed set the model's __unicode__ function

class userInfo(models.Model):
  #model fields

  def __unicode__(self):
    return self.auth.username

Python – the difference between null=True and blank=True in Django

null=True sets NULL (versus NOT NULL) on the column in your DB. Blank values for Django field types such as DateTimeField or ForeignKey will be stored as NULL in the DB.

blank determines whether the field will be required in forms. This includes the admin and your custom forms. If blank=True then the field will not be required, whereas if it's False the field cannot be blank.

The combo of the two is so frequent because typically if you're going to allow a field to be blank in your form, you're going to also need your database to allow NULL values for that field. The exception is CharFields and TextFields, which in Django are never saved as NULL. Blank values are stored in the DB as an empty string ('').

A few examples:

models.DateTimeField(blank=True) # raises IntegrityError if blank

models.DateTimeField(null=True) # NULL allowed, but must be filled out in a form

Obviously, Those two options don't make logical sense to use (though there might be a use case for null=True, blank=False if you want a field to always be required in forms, optional when dealing with an object through something like the shell.)

models.CharField(blank=True) # No problem, blank is stored as ''

models.CharField(null=True) # NULL allowed, but will never be set as NULL

CHAR and TEXT types are never saved as NULL by Django, so null=True is unnecessary. However, you can manually set one of these fields to None to force set it as NULL. If you have a scenario where that might be necessary, you should still include null=True.

Best Solution

Related Solutions

Python – django – inlineformset_factory with more than one ForeignKey

Python – the difference between null=True and blank=True in Django

Related Question