Calculates (interpolated) average grade

grader.py

#!/usr/bin/env python2

from itertools import izip, count
from math import fsum, ceil, floor
import fileinput

GRADES = ("FL", "PC", "PS", "CR", "DN", "HD")
MARKS = dict(izip(GRADES, count()))

def average(seq):
   return fsum(seq)/len(seq)

def interpolated_grade(mark):
    upper = int(ceil(mark))
    lower = int(floor(mark))
    grade = GRADES[lower]
    if lower != upper:
        grade += "/%s" % GRADES[upper]
    return grade

mark = average([average([MARKS[grade] for grade in line.strip().split('/')]) for line in fileinput.input()])
print "%s (%.1f)" % (interpolated_grade(mark), mark)