Post values from an HTML form and access them in a Flask view

I have an HTML form that gets posted to a Flask route. However, request.form is empty. If I try to access one of the values by id, I get a 400 error. How do I post values from an HTML form and access them in Flask?

<form method="POST">
  <input id="my_input" type="text" value="{{ email }}">
  <input id="my_submit" type="submit" value="Submit">
</form>

@app.route('/page', methods=['POST', 'GET'])
def get_page():
    if request.method == 'POST':
        print(request.form)  # prints ImmutableMultiDict([])
        print(request.form['my_input'])  # raises 400 error
    return render_template('page.html')

Your input doesn't have a name attribute. That is what the client will pass along to the server. Flask will raise a 400 error if you access a form key that wasn't submitted.

<input name="my_input" id="my_input" type="text" value="{{ email }}">