fields.py

from django import forms
# import models here from django and subclass
from django.db import models
from django.template.defaultfilters import filesizeformat
from django.utils.translation import ugettext_lazy as _
from django.conf import settings

class RestrictedFileFieldModel(models.FileField):
    def __init__(self, *args, **kwargs):
        self.content_types = kwargs.pop('content_types', None)
        self.max_upload_size = kwargs.pop('max_upload_size', None)
        if not self.max_upload_size:
            self.max_upload_size = settings.MAX_UPLOAD_SIZE
        super(RestrictedFileField, self).__init__(*args, **kwargs)

    def clean(self, *args, **kwargs):
        data = super(RestrictedFileField, self).clean(*args, **kwargs)
        try:
            if data.content_type in self.content_types:
                if data.size > self.max_upload_size:
                    raise forms.ValidationError(_('File size must be under %s. Current file size is %s.') % (filesizeformat(self.max_upload_size), filesizeformat(data.size)))
            else:
                raise forms.ValidationError(_('File type (%s) is not supported.') % data.content_type)
        except AttributeError:
            pass

        return data

class RestrictedFileField(forms.FileField):
    def __init__(self, *args, **kwargs):
        self.content_types = kwargs.pop('content_types', None)
        self.max_upload_size = kwargs.pop('max_upload_size', None)
        if not self.max_upload_size:
            self.max_upload_size = settings.MAX_UPLOAD_SIZE
        super(RestrictedFileField, self).__init__(*args, **kwargs)

    def clean(self, *args, **kwargs):
        data = super(RestrictedFileField, self).clean(*args, **kwargs)
        try:
            if data.content_type in self.content_types:
                if data.size > self.max_upload_size:
                    raise forms.ValidationError(_('File size must be under %s. Current file size is %s.') % (filesizeformat(self.max_upload_size), filesizeformat(data.size)))
            else:
                raise forms.ValidationError(_('File type (%s) is not supported.') % data.content_type)
        except AttributeError:
            pass

        return data

class RestrictedImageField(forms.ImageField):
    def __init__(self, *args, **kwargs):
        self.max_upload_size = kwargs.pop('max_upload_size', None)
        if not self.max_upload_size:
            self.max_upload_size = settings.MAX_UPLOAD_SIZE
        super(RestrictedImageField, self).__init__(*args, **kwargs)

    def clean(self, *args, **kwargs):
        data = super(RestrictedImageField, self).clean(*args, **kwargs)
        try:
            if data.size > self.max_upload_size:
                raise forms.ValidationError(_('File size must be under %s. Current file size is %s.') % (filesizeformat(self.max_upload_size), filesizeformat(data.size)))
        except AttributeError:
            pass

        return data