example1:

a = list(input('Слово:'))

b = {}

for c in a:

   try: b[c] += 1

   except KeyError: b[c] = 1

for a1, a2 in b.items():

   print(a1,':',a2)

example2:

a = list(input('Слово:'))

b = {i: a.count(i) for i in a}

for a1, a2 in b.items():

   print(a1,':',a2)

example3:

a = list(input('Слово:'))

b = reduce(lambda x,y: dict(x.items()+[(y,x[y]+1 if y in x else 1)]), a, dict())

for a1, a2 in b.items():

   print(a1,':',a2)