created new function to verify ISBN in models.py

nishaespera_reading/bookshelf/models.py

@@ -13,9 +13,11 @@ class Author(models.Model):
     def __str__(self):
         return self.first_name + ' ' + self.last_name
 
-def verify_int(value):
+def verify_ISBN(value):
     if value.isdigit() == False:
         raise ValidationError('ISBN must only be integers.')
+    if value != 13:
+        raise ValidationError('ISBN must be a 13 digit number.')
     
 def verify_wordCount(value):
     word_count = int(len(value.split()))
@@ -31,7 +33,7 @@ class Books(models.Model):
     year_published = models.IntegerField(null = True, blank = True,
         validators=[MinValueValidator(1000), MaxValueValidator(datetime.now().year)]
         )
-    ISBN = models.CharField(max_length = 13, validators = [MinValueValidator(13), verify_int])
+    ISBN = models.CharField(validators = [verify_ISBN])
     blurb = models.TextField(validators = [verify_wordCount])
     
     def __str__(self):