You have a string with many consecutive letters: "aabbaadddc". Write a function that compresses the string by counting the consecutive letters. (If there is only one letter, it should resolve to itself). "aaaaabbaadddc" -> "a5b2a2d3c"

gistfile1.txt

#"aabbbcccdde" => "a2b3c3d2e1"


def encode_string(unencoded):

  if unencoded is None or unencoded == "":
    return None

  last_letter = None
  count = 0
  result = ""

  for letter in unencoded:
    if last_letter is None:
      last_letter = letter
      count = 1
      continue

    if letter == last_letter:
      count += 1

    else:
      if count == 1:
        result += last_letter
      else:
        result += "{0}{1}".format(last_letter, count)
      last_letter = letter
      count = 1


  if count == 1:
    result += last_letter
  else:
    result += "{0}{1}".format(last_letter, count)

  return result

def decode_string(encoded):

  result = ""

  numbers = [str(i) for i in range(1, 10)]

  i = 0

  while i < len(encoded):

    letter = encoded[i]

    try:
      count = encoded[i+1]
    except IndexError:
      count = None

    if count and count in numbers:
      result += letter * int(count)
      i += 2
    else:
      result += letter
      i += 1


  return result

print encode_string("aabbbcccdd")
print encode_string("xyz")
print encode_string("aabbbcccdde")
assert encode_string("aabbbcccdde") == "a2b3c3d2e"

print decode_string("a2b3c3d2e")
print decode_string("ab3cz3d2e")
print decode_string("xyz")

assert "aabbbcccdde" == decode