Use locale.format() on the integer, but beware of the current locale on your environment. Some environments may not have this set or set to something that won't give you a commafied result.
Here's some code I had to write to deal with this exact issue. It'll automatically set the locale for you depending on your platform:
try:
locale.setlocale(locale.LC_ALL, 'en_US.UTF-8') #use locale.format for commafication
except locale.Error:
locale.setlocale(locale.LC_ALL, '') #set to default locale (works on windows)
score = locale.format('%d', player['score'], True)