Re: Weird date math bug?

On Aug 31, 2017 9:44 PM, "Lachlan Musicman" <datakid@gmail.com> wrote:

Sorry, let me start again:

Yay, I'm not the only one that does it! Lol...

<snip>

class ChemoRegime(models.Model):
    patient = models.ForeignKey(Patient, on_delete=models.CASCADE)
    chemotype = models.ForeignKey(ChemoType, on_delete=models.CASCADE)
    start_date = models.DateField(null=True, blank=True)
    stop_date = models.DateField(null=True, blank=True)

    def regime_age(self):
        age = timezone.now().date() - self.stop_date
        return age.days

<snip>

But in the browser:

Exception Type:     TypeError
Exception Value:    

unsupported operand type(s) for -: 'datetime.date' and 'NoneType'

Exception Location:     ./patients/models.py in regime_age, line 95

line 95 is         age = timezone.now().date() - self.stop_date

What am I doing wrong?

cheers

L.

I'm guessing that ChemoRegime.regime_age() contains line 95.

ChemoRegime defines the stop_date field with null=True and blank=True. I'm guessing this is because patients may not have yet stopped treatment, so they have no stop_date.

With that in mind, self.stop_date may be None in Python (and Null in the DB). Subtracting None from a real datetime.date object is not supported.

Ensure that stop_date has a date value before doing date math with it.

-James

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