input: Write a function to create an HTML form with a submit button that sends information to a Python program. The form should use the POST method and the action should point to a Python program named 'action.py'. If the input is empty, the function should return the form without any additional fields. If the input contains additional form fields, they should be included in the form.
  assert create_html_form([])=='<form action="action.py" method="post"><input type="submit" value="Submit"></form>'
  assert create_html_form(['<input type="text" name="username">'])=='<form action="action.py" method="post"><input type="text" name="username"><input type="submit" value="Submit"></form>'
  assert create_html_form(['<input type="password" name="password">','<input type="email" name="email">'])=='<form action="action.py" method="post"><input type="password" name="password"><input type="email" name="email"><input type="submit" value="Submit"></form>'
output: def create_html_form(fields):
      form_fields = ''.join(fields)
      return f'<form action="action.py" method="post">{form_fields}<input type="submit" value="Submit"></form>'