A form field to handle validation of image + svg.

svgimagefield.py

from xml.etree import cElementTree as et

from django.core.exceptions import ValidationError
from django.forms import ImageField


class SVGImageField(ImageField):
    """A Django ImageField that accepts SVG images."""
    def to_python(self, data):
        """
        Check that the file-upload field data contains a valid image
        (GIF, JPG, PNG, etc. -- whatever Pillow supports) or a SVG image.
        """
        try:
            file = super(SVGImageField, self).to_python(data)
        except ValidationError as err:
            # add a workaround to handle svg images
            if not self.is_svg(file):
                raise ValidationError(
                    self.error_messages['invalid_image'],
                    code='invalid_image',
                ) from err
            file = super(ImageField, self).to_python(data)
            file.content_type = 'image/svg+xml'
        return file

    def run_validators(self, value: str):
        if not self.is_svg(value):
            return super(ImageField, self).run_validators(value)
        return super(SVGImageField, self).run_validators(value)

    @staticmethod
    def is_svg(file):
        """Check if the provided file is a SVG image."""
        file = file.seek(0) if hasattr(file, 'seek') else open(file)
        try:
            tag = '{http://www.w3.org/2000/svg}svg'
            iter = et.iterparse(file, ('start',))
            return next(iter)[1].tag == tag
        except et.ParseError:
            return False
        finally:
            file.close()