title: How to make Min/MaxValueValidator work with Django's DecimalField?
body: <p>A strange failure seems to occur in Django 2.1.2 (Python 3.7.0):</p>
  
  <pre><code>from django.db.models import DecimalField
  from django.core.validators import MaxValueValidator, MinValueValidator
  f = DecimalField(max_digits=4, decimal_places=2, validators=[MinValueValidator(10), MaxValueValidator(20)])
  </code></pre>
  
  <p>This is the expected behavior:</p>
  
  <pre><code>&gt;&gt;&gt; f.clean(15, model_instance=None)
  Decimal('15')
  &gt;&gt;&gt; f.clean('15', model_instance=None)
  Decimal('15')
  </code></pre>
  
  <p>But this doesn't work:</p>
  
  <pre><code>&gt;&gt;&gt; f.clean(5, model_instance=None)
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
    File "/Users/.../anaconda3/envs/django/lib/python3.7/site-packages/django/db/models/fields/__init__.py", line 632, in clean
      self.run_validators(value)
    File "/Users/.../anaconda3/envs/django/lib/python3.7/site-packages/django/db/models/fields/__init__.py", line 591, in run_validators
      raise exceptions.ValidationError(errors)
  django.core.exceptions.ValidationError: &lt;exception str() failed&gt;
  </code></pre>
  
  <p>Same error for:</p>
  
  <pre><code>&gt;&gt;&gt; f.clean('5', model_instance=None)
  &gt;&gt;&gt; f.clean(25, model_instance=None)
  </code></pre>
  
  <p>What am I doing wrong?</p>
  
  <p>NB: I know how to validate this field manually in the ModelForm, but I would prefer to avoid the workaround. I have checked some related answers with no success:</p>
  
  <ul>
  <li><a href="https://stackoverflow.com/questions/40322802/decimalfield-validation-in-django">DecimalField Validation in Django</a></li>
  <li><a href="https://stackoverflow.com/questions/34578193/minvaluevalidator-not-working-on-decimalfield-in-django">MinValueValidator not working on DecimalField in Django</a></li>
  <li><a href="https://stackoverflow.com/questions/52376693/django-strange-decimalfield-validation">Django strange DecimalField validation</a></li>
  </ul>