Pygame triangle collision detection

Typically 2D collisions are implemented as squares in most games development frameworks. They are called "collision boxes" or "hit boxes". You could install a PyGame extension such as Pylygon to handle polygon collisions, or alternatively there is a much simpler solution:

Use multiple collision boxes on your triangle object, several small squares could map the collision detection fairly closely to the actual visual's profile. Of course this isn't going to be "pixel perfect" but it typically works pretty well, of course if you need very accurate collisions this way wouldn't suit it.

Here's a picture to illustrate what I mean by that: