Selenium django HTML functional test move to next input

Looking at: http://ift.tt/1KdDIDn

it appear that you can move between input fields with those Keys, I've tried:

    elem = self.browser.find_element_by_id("base") # find first input field
    elem.send_keys("1234,5")           # compile data
    elem=elem.send_keys(Keys.TAB)      # move to next
    elem.send_keys("456,5")            # compile data

but this get an error, because elem=elem.send_keys(Keys.TAB) isn't the next input field.

How can I move to next input field and compile it, without recreate the element object with find_element_by...?