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

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'
        })

Check this page

city = forms.CharField(widget=forms.TextInput(attrs={'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

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>