Hello,

Use something like below, it will automatically download the file:

import base64
# output is where you have the content of your file, it can be
# any type of content
output 
# encode
result = base64.b64encode(output.read())
# get base url
base_url = self.env['ir.config_parameter'].get_param('web.base.url')
attachment_obj = self.env['ir.attachment']
# create attachment
attachment_id = attachment_obj.create(
	{'name': "name", 'datas_fname': 'name.file_ext', 'datas': result})
# prepare download url
download_url = '/web/content/' + str(attachment_id.id) + '?download=true'
# download
return {
	"type": "ir.actions.act_url",
	"url": str(base_url) + str(download_url),
	"target": "new",
}