compress.py

def compress(stringy):
    prvChr = ""
    newStr = ""
    matchCnt = 1
    lenny = len(stringy)
    for i in range(lenny):
        # if not the last char in the string
        if i != lenny-1:
            # if current char equals next char
            if stringy[i] == stringy[i + 1]:
                matchCnt += 1
            # else end of a matching sequence
            else:
                newStr += str(matchCnt)
                newStr += stringy[i]
                matchCnt=1
        # the last char of the string
        else:
            newStr += str(matchCnt)
            newStr += stringy[i]
            matchCnt=1
            
    return newStr



myString = "aaaaaaBBBB***aa"

print compress(myString)