<p>The reason behind this is that Django's <code>ValidationError</code> class is intended for use with HTML forms and its API makes using it slightly awkward with nested validation errors that can occur in serializers.</p>

<p>For most users this change shouldn't require any updates to your codebase, but it is worth ensuring that whenever raising validation errors you should prefer using the <code>serializers.ValidationError</code> exception class, and not Django's built-in exception.</p>

<p>We strongly recommend that you use the namespaced import style of <code>import serializers</code> and not <code>from serializers import ValidationError</code> in order to avoid any potential confusion.</p>

<p>The <code>validate_&lt;field_name&gt;</code> method hooks that can be attached to serializer classes change their signature slightly and return type. Previously these would take a dictionary of all incoming data, and a key representing the field name, and would return a dictionary including the validated data for that field:</p>

<pre><code>def validate_score(self, attrs, source):

if attrs['score'] % 10 != 0:

raise serializers.ValidationError({'my_field': 'A field error'})

<p>This ensures you can still write validation that compares all the input fields, but that marks the error against a particular field.</p>

<p>The under-used <code>transform_&lt;field_name&gt;</code> on serializer classes is no longer provided. Instead you should just override <code>to_representation()</code> if you need to apply any modifications to the representation style.</p>

<p>For example:</p>

<pre><code>def to_representation(self, instance):

<hr />

<h2 id="39x-series"><a class="toclink" href="#39x-series">3.9.x series</a></h2>

<h3 id="393"><a class="toclink" href="#393">3.9.3</a></h3>

<p><strong>Date</strong>: [29th April 2019]</p>

<p>This is the last Django REST Framework release that will support Python 2.

<li>Added regex style to <code>SearchFilter</code>. (<a href="https://github.com/encode/django-rest-framework/issues/3316">#3316</a>)</li>

<li>Resolve issues with setting blank HTML fields. (<a href="https://github.com/encode/django-rest-framework/issues/3318">#3318</a>) (<a href="https://github.com/encode/django-rest-framework/issues/3321">#3321</a>)</li>

<li>Correctly display existing 'select multiple' values in browsable API forms. (<a href="https://github.com/encode/django-rest-framework/issues/3290">#3290</a>)</li>

<li>Fix to ensure admin renderer continues to work when pagination is disabled. (<a href="https://github.com/encode/django-rest-framework/issues/3275">#3275</a>)</li>

<li>Resolve error with <code>LimitOffsetPagination</code> when count=0, offset=0. (<a href="https://github.com/encode/django-rest-framework/issues/3303">#3303</a>)</li>