Compressing python strings

from collections import Counter
from itertools import chain


def compress(value):
    counter = Counter(value)
    return "".join(str(v) for v in chain.from_iterable(counter.items()))


assert compress("aabbbccccddaa") == "a4b3c4d2"

 a = list(input())

 def k(c):

     b = 0
     for i in range(len(a)-1):
         b += a.count(a[i])
         For j in range(len(a), 0, -1):#Length????
             if a.count(a[i]) != 1:
                 del a[i]
         return b == 1
         print(a[i]+b,end="")
 print(k(a))