Where in the code is the is_valid method checked?

The is_valid method is typically used in data validation contexts, such as in Django REST Framework serializers. The call to is_valid() usually occurs in the code that handles incoming data processing, often in views or controllers, before saving or further processing the data.

Example:

serializer = MySerializer(data=request.data)
if serializer.is_valid():
    # Data is valid, can save or use
    serializer.save()
else:
    # Handle validation errors
    return Response(serializer.errors, status=400)

Thus, the call to is_valid() happens in the code responsible for receiving and processing data, to ensure data correctness before further actions.