Html:

<script>
    grecaptcha.ready(function() {
        grecaptcha.execute(<KEY>, {action: ''})
        .then(function(token) {
            ginput = document.createElement('input');
            ginput.type = "hidden";
            ginput.name = "g-recaptcha-response";
            ginput.value = token;
            document.getElementById("cform").appendChild(ginput);
        });
    });
</script>

<form id='cform' role="form" action="" method="post">
    {% csrf_token %}
    {{ form.as_p }}

    <script src='https://www.google.com/recaptcha/api.js?render=<KEY>'></script>
    <div class="g-recaptcha" data-sitekey=<KEY>></div>

    <button type="submit">Submit</button>
</form>


Views.py:

def contact(request):
    form_class = ContactForm

    if request.method == 'POST':
        form = form_class(data=request.POST)

        if form.is_valid():

            recaptcha_response = request.POST.get('g-recaptcha-response')
            url = 'https://www.google.com/recaptcha/api/siteverify'
            payload = {
                'secret': settings.GOOGLE_RECAPTCHA_SECRET_KEY,
                'response': recaptcha_response
            }
            data = urllib.parse.urlencode(payload).encode()
            req = urllib.request.Request(url, data=data)

            response = urllib.request.urlopen(req)
            result = json.loads(response.read().decode())

            if (not result['success']) or (not result['action'] == ''):
                messages.error(request, 'Invalid reCAPTCHA. Please try again.')

            contact_name = request.POST.get(
                'contact_name'
            , '')
            contact_email = request.POST.get(
                'contact_email'
            , '')
            form_content = request.POST.get('content', '')

            # Email the profile with the
            # contact information
            template = get_template('contact_template.txt')
            context = {
                'contact_name': contact_name,
                'contact_email': contact_email,
                'form_content': form_content,
            }
            content = template.render(context)

            email = EmailMessage(
                "New contact form submission",
                content,
                "Your website" +'',
                ['GMAIL_EMAIL'],
                headers = {'Reply-To': contact_email }
            )
            email.send()
            messages.info(request, "Success")

    return render(request, 'contact.html', {
        'form': form_class,
    })