Web scraping with python's request module requires submit button

I'm trying to web scrape my grades off of this website.

I have this which enters the login info (I think):

import requests
def main():
    login = {'username':'USERNAME', 'password':'PASSWORD'}
    url = 'https://parent-portland.cascadetech.org/portland/Login_Parent_PXP.aspx?regenerateSessionId=True'
    r = requests.post(url, login)
    r.submit()
    print(r.text)
main()

It looks like you have to press a button.

<input name="Submit1" id="Submit1" value="Login" cssclass="btn" text="Login" onclick="this.disabled=true;this.form.submit();" type="submit">

However, I just learned this today and I have no idea how to do this with the requests module.