Django: How do I add arbitrary html attributes to input fields on a form?

I have an input field that is rendered with a template like so:

<div class="field">
   {{ form.city }}
</div>

Which is rendered as:

<div class="field">
    <input id="id_city" type="text" name="city" maxlength="100" />
</div>

Now suppose I want to add an autocomplete="off" attribute to the input element that is rendered, how would I do that? Or onclick="xyz()" or class="my-special-css-class"?

Check this page

city = forms.CharField(widget=forms.TextInput(attrs={'autocomplete':'off'}))

Sorry for advertisment, but I've recently released an app (https://github.com/kmike/django-widget-tweaks) that makes such tasks even less painful so designers can do that without touching python code:

{% load widget_tweaks %}
...
<div class="field">
   {{ form.city|attr:"autocomplete:off"|add_class:"my_css_class" }}
</div>

or, alternatively,

{% load widget_tweaks %}
...
<div class="field">
   {% render_field form.city autocomplete="off" class+="my_css_class" %}
</div>

If you are using "ModelForm":

class YourModelForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        super(YourModelForm, self).__init__(*args, **kwargs)
        self.fields['city'].widget.attrs.update({
            'autocomplete': 'off'
        })

If you are using ModelForm, apart from the possibility of using __init__ as @Artificioo provided in his answer, there is a widgets dictionary in Meta for that matter:

class AuthorForm(ModelForm):
    class Meta:
        model = Author
        fields = ('name', 'title', 'birth_date')
        widgets = {
            'name': Textarea(attrs={'cols': 80, 'rows': 20}),
        }

Relevant documentation

I did't want to use an entire app for this thing. Instead I found the following code here https://blog.joeymasip.com/how-to-add-attributes-to-form-widgets-in-django-templates/

# utils.py
from django.template import Library
register = Library()

@register.filter(name='add_attr')
def add_attr(field, css):
    attrs = {}
    definition = css.split(',')

    for d in definition:
        if ':' not in d:
            attrs['class'] = d
        else:
            key, val = d.split(':')
            attrs[key] = val

    return field.as_widget(attrs=attrs)

use the tag in the html file

{% load utils %}
{{ form.field_1|add_attr:"class:my_class1 my_class2" }}
{{ form.field_2|add_attr:"class:my_class1 my_class2,autocomplete:off" }}

I have spent quite a few days trying to create re-usable form templates to create and update models in Django forms. Note that am using ModelForm to change or create object. Am using also bootstrap to style my forms. I used django_form_tweaks for some forms in past, but I needed some customization without a lot of template dependency. Since I already have jQuery in my Project I decided to leverage its properties to style my forms. Here is the code, and can work with any form.

#forms.py
from django import forms
from user.models import User, UserProfile
from .models import Task, Transaction

class AddTransactionForm(forms.ModelForm):
    class Meta:
       model = Transaction
       exclude = ['ref_number',]
       required_css_class = 'required'

Views.py

@method_decorator(login_required, name='dispatch')
class TransactionView(View):
def get(self, *args, **kwargs):
    transactions = Transaction.objects.all()
    form = AddTransactionForm
    template = 'pages/transaction.html'
    context = {
        'active': 'transaction',
        'transactions': transactions,
        'form': form
    }
    return render(self.request, template, context)

def post(self, *args, **kwargs):
    form = AddTransactionForm(self.request.POST or None)
    if form.is_valid():
        form.save()
        messages.success(self.request, 'New Transaction recorded succesfully')
        return redirect('dashboard:transaction')
    messages.error(self.request, 'Fill the form')
    return redirect('dashboard:transaction')

HTML Code Note: Am using bootstrap4 modal to remove the hassle of creating many views. Maybe it is better to use generic CreateView or UpdateView. Link Bootstrap and jqQery

 <div class="modal-body">
    <form method="post" class="md-form" action="." enctype="multipart/form-data">
      {% csrf_token %}
      {% for field in form %}
      <div class="row">
        <div class="col-md-12">
          <div class="form-group row">
            <label for="" class="col-sm-4 col-form-label {% if field.field.required %}
            required font-weight-bolder text-danger{%endif %}">{{field.label}}</label>
            <div class="col-sm-8">
              {{field}}
            </div>

          </div>
        </div>
      </div>

      {% endfor %}

      <input type="submit" value="Add Transaction" class="btn btn-primary">
    </form>
  </div>

Javascript Code remember to load this in $(document).ready(function() { /* ... */}); function.

var $list = $("#django_form :input[type='text']");
$list.each(function () {
    $(this).addClass('form-control')
  });
  var $select = $("#django_form select");
  $select.each(function () {
    $(this).addClass('custom-select w-90')
  });
  var $list = $("#django_form :input[type='number']");
  $list.each(function () {
    $(this).addClass('form-control')
  });
  var $list = $("form :input[type='text']");
  $list.each(function () {
    $(this).addClass('form-control')
  });
  var $select = $("form select");
  $select.each(function () {
    $(this).addClass('custom-select w-90')
  });
  var $list = $("form :input[type='number']");
  $list.each(function () {
    $(this).addClass('form-control')
  });