Posting Data on Flask via form is giving 400 Bad Request
Ah, I think I see it: You only set the id but not the name for the input element. Yet the name is used in the form data that is sent to the server. This causes a KeyError at request.form['query'] which causes the 400 error.
Besides what @Robin Krahl said, You also should add enctype="multipart/form-data" in your form. So the code maybe like this:
<form id="form1" action="/final" method="post" enctype="multipart/form-data"> <input id='query' type="text"> <button type="submit" onClick='sub()'>Submit ยป</button></form>"