file_upload.pt

<tal:block tal:define="oid oid|field.oid;
        css_class css_class|field.widget.css_class;
        style style|field.widget.style;">
${field.start_mapping()}
    <input type="file" name="upload" id="${oid}"
             tal:attributes="style style;
                    accept accept|field.widget.accept;
                    data-filename cstruct.get('filename');
                    attributes|field.widget.attributes|{};"/>
    <input tal:define="uid cstruct.get('uid')"
             tal:condition="uid"
            type="hidden" name="uid" value="${uid}"/>
    <a tal:define="preview_url cstruct.get('preview_url');
            filename cstruct.get('filename')"
             tal:condition="preview_url" href="${structure: preview_url}"
    target="_blank">Show</a>

        ${field.end_mapping()}
    <script type="text/javascript">
        deform.addCallback('${oid}', function (oid) {
            $('#' + oid).upload();
        });
    </script>
</tal:block>