[Django] Dynamically require a field

form.py

from django import forms

class MyForm(forms.Form):
    def clean(self):
        is_something = cleaned_data.get('is_something')
        if is_something:
            validate_required_field(self, cleaned_data, 'name_of_dynamically_required_field')

utils.py

from django.core.validators import EMPTY_VALUES

def validate_required_field(form, cleaned_data, field_name, message="This field is required."):
    """
    Mark a field as required if not present or empty
    :type form: django.forms.Form
    :param form: The form
    :type cleaned_data: dict
    :param cleaned_data: The form cleaned data
    :type field_name: str
    :param field_name: The required field name
    :type message: str
    :param message: The error message. Default to `The field is required`.
    :rtype: None
    :return: Nothing
    """

    missing_field = field_name not in cleaned_data
    empty_field = not missing_field and cleaned_data[field_name] in EMPTY_VALUES
    if missing_field or empty_field:
        form.add_error(field_name, message)