A form field to handle validation of image + svg, Django 3.1

svgimagefield.py

from django.core import validators
from lxml import etree

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


# monkeypatch allowed file extensions:
_original = validators.get_available_image_extensions
validators.get_available_image_extensions = lambda: _original() + ["svg"]


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.
        """
        file = super(ImageField, self).to_python(data)  # skip a MRO level
        if file is None:
            return None
        try:
            file = super().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().run_validators(value)

    @staticmethod
    def is_svg(file):
        """Check if the provided file is a SVG image."""
        if file is None:
            return False
        if hasattr(file, 'seek'):
            file.seek(0)
            opened = False
        else:
            file = open(file)
            opened = True
        try:
            part_of_svg_tag = '{http://www.w3.org/2000/svg}'
            tree = etree.iterparse(file)
            first_tag = next(tree)[1].tag
            return part_of_svg_tag in first_tag
        except etree.ParseError:
            return False
        finally:
            if opened:
                file.close()