<form name="login" id="form1" method="post" action="http://mylogin.net">
  Username: <input name="username" id="input1" type="text" /><br/>
  Password: <input name="password" id="input2" type="password" /><br/>
  <input type="submit" value="OK" />
</form>

r = requests.post( loginUrl, data = {'input1':'myuser', 'input2':'mypw'} ) ?