forms.py

"""Allows checking of form POST data as well as uploaded files when validating
a standard Django `forms.Form`.

The short version is that you check `Form().files` in the `clean()` method, 
assuming the form has been bound to the request.

See:
http://mattoc.com/django-handle-form-validation-with-combined-post-and-files-data/
"""

from django import forms


class BannerUploadForm(forms.Form):
    banner = forms.FileField()
    placeholder_text = forms.CharField()

    def clean(self):
        cleaned_data = super(BannerUploadForm, self).clean()

        text = cleaned_data.get('placeholder_text')

        if not text and not 'banner' in self.files:
            raise forms.ValidationError('Please upload a banner image or '
                    'add placeholder text.')

        return cleaned_data

upload.html

{% extends 'base.html' %}

{% block content %}
<form method="post" action="{% url upload-banner %}" enctype="multipart/form-data">{% csrf_token %}
    {{ form.as_p }}
    <input type="submit" value="Upload">
</form>
{% endblock content %}

urls.py

url(r'^banner/upload/$', 'banners.views.upload_banner', name='upload-banner')

views.py

from django.shortcuts import render

from .forms import BannerUploadForm


def upload_banner(request):
    template_name = 'banners/upload.html'
    context = {}

    if request.method == 'POST':
        # request.FILES must be bound to form else form.files will be empty
        form = BannerUploadForm(request.POST, request.FILES)

        if form.is_valid():
            # your handler here
            template_name = 'banners/success.html'
    else:
        form = BannerUploadForm()

    context['form'] = form
    
    return render(request, template_name, context)