Average of string & missing values in dictionary (python)

Question

I have a dictionary whereas the values are of string type. But I want to calculate the average per key whereas the empty string is a missing value. Here's my code just need a small twerk for it to work...with error : int() argument must be a string or a number, not 'list'

dic = {'E': ['1', '', '3'], 'M': ['2', '', '1']}
for k,n in dic.items():
    k = [0]
    n = [1]

D = {k: (int(n)) for k, n in dic.items() if n}
ave = {k:sum(D)/float(len(D))} if D else '-'
print ave

Expected output: {'E': 2, 'M': 1.5}

Answer 1

dic = {'E': ['1', '', '3'], 'M': ['2', '', '1']}
ave = dict()
for k in dic:
   nonempty = [ float(v) for v in dic[k] if v != '' ]
   ave[k] = sum(nonempty) / len(nonempty)
print ave