boards/forms/fields.py

from django import forms
from django.utils.translation import ugettext_lazy as _, ungettext_lazy


ATTRIBUTE_PLACEHOLDER = 'placeholder'


class UrlFileWidget(forms.MultiWidget):
    def __init__(self, *args, **kwargs):
        widgets = (
                forms.ClearableFileInput(attrs={'accept': 'file/*'}),
                forms.TextInput(attrs={ATTRIBUTE_PLACEHOLDER:
                    'http://example.com/image.png'}),
        )
        super().__init__(widgets, *args, **kwargs)

    def decompress(self, value):
        return [None, None]


class UrlFileField(forms.MultiValueField):
    widget = UrlFileWidget

    def __init__(self, *args, **kwargs):
        fields = (
                forms.FileField(required=False, label=_('File'),
                    widget=forms.ClearableFileInput(
                        attrs={'accept': 'file/*'})),
                forms.CharField(required=False, label=_('File URL'),
                    widget=forms.TextInput(
                        attrs={ATTRIBUTE_PLACEHOLDER:
                            'http://example.com/image.png'})),
        )

        super().__init__(
                fields=fields,
                require_all_fields=False, *args, **kwargs)

    def compress(self, data_list):
        if data_list and len(data_list) >= 2:
           return data_list[0] or data_list[1]