Django set range for integer model field as constraint

You can use Django’s built-in validators –

from django.db import models
from django.core.validators import MaxValueValidator, MinValueValidator

class MyModel(models.Model):
    qty = models.IntegerField(
        default=1,
        validators=[MaxValueValidator(100), MinValueValidator(1)]
     )

NOTE:

1. The validators will not run automatically when you save a model, but if you are using a ModelForm, it will run your validators on the fields that are included in the form. Check this link for more info.
2. To enforce constraints on a database level refer to maertejin’s answer below.