'unicode' is not defined with alpine

[FabriceMailleferObjectis]

I got the following error when generating a PDF from HTML with the "alpine" tag:

[2022-05-20 08:10:41,195] ERROR in app: Exception on /pdf [POST]
Traceback (most recent call last):
File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1982, in wsgi_app
response = self.full_dispatch_request()
File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1614, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1517, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
raise value
File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1612, in full_dispatch_request
rv = self.dispatch_request()
File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1598, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "app.py", line 15, in pdf
doc = handle_request(config)
File "app.py", line 44, in handle_request
pdf = pdfkit.from_string(unicode(request.form['html']), output_path=False, configuration=config, options=options)
NameError: name 'unicode' is not defined

I tried with the docker image with "latest" tag based on Debian, it works as expected.

How can I update the dockerfile or app.py to make it works also on alpine?