Here’s a possible solution:
def merge_lists(l1, l2, key):
merged = {}
for item in l1+l2:
if item[key] in merged:
merged[item[key]].update(item)
else:
merged[item[key]] = item
return merged.values()
courses = merge_lists(user_course_score, courses, 'course_id')
Produces:
[{'course_id': 1456, 'name': 'History', 'score': 56},
{'course_id': 316, 'name': 'Science', 'score': 71},
{'course_id': 926, 'name': 'Geography'}]
As you can see, I used a dictionary (‘merged’) as a halfway point. Of course, you can skip a step by storing your data differently, but it depends also on the other uses you may have for those variables.
All the best.