onchange

html

<select onchange="this.form.submit()">
    ...
</select>

django-crispy-forms

self.helper.layout = Layout(
    Field('select_field', onchange="this.form.submit()")
)

onkeyup

django-crispy-forms

self.helper.layout = Layout(
    Field('select_field', onkeyup="this.form.submit()")
)