Python递归实现字符串的压缩与解压缩算法

def compress_str(s):
    if len(s) == 0:
        return ''
    elif len(s) == 1:
        return s + '1'
    else:
        count = 1
        compressed_str = ''
        for i in range(1, len(s)):
            if s[i] == s[i-1]:
                count += 1
            else:
                compressed_str += s[i-1] + str(count)
                count = 1
        compressed_str += s[i] + str(count)
        return compressed_str

def decompress_str(s):
    if len(s) == 0:
        return ''
    else:
        decompressed_str = ''
        i = 0
        while i < len(s):
            c = s[i]
            count = 0
            i += 1
            while i < len(s) and s[i].isdigit():
                count = count * 10 + int(s[i])
                i += 1
            decompressed_str += c * count
        return decompressed_str