Task: Run-length encoding
C: #include <stdio.h>
#include <stdlib.h>

typedef struct stream_t stream_t, *stream;
struct stream_t {
	
	int (*get)(stream);
	
	int (*put)(stream, int);
};


typedef struct {
	int (*get)(stream);
	int (*put)(stream, int);
	char *string;
	int pos;
} string_stream;

typedef struct {
	int (*get)(stream);
	int (*put)(stream, int);
	FILE *fp;
} file_stream;


int sget(stream in)
{
	int c;
	string_stream* s = (string_stream*) in;
	c = (unsigned char)(s->string[s->pos]);
	if (c == '\0') return -1;
	s->pos++;
	return c;
}

int sput(stream out, int c)
{
	string_stream* s = (string_stream*) out;
	s->string[s->pos++] = (c == -1) ? '\0' : c;
	if (c == -1) s->pos = 0;
	return 0;
}

int file_put(stream out, int c)
{
	file_stream *f = (file_stream*) out;
	return fputc(c, f->fp);
}


void output(stream out, unsigned char* buf, int len)
{
	int i;
	out->put(out, 128 + len);
	for (i = 0; i < len; i++)
		out->put(out, buf[i]);
}


void encode(stream in, stream out)
{
	unsigned char buf[256];
	int len = 0, repeat = 0, end = 0, c;
	int (*get)(stream) = in->get;
	int (*put)(stream, int) = out->put;

	while (!end) {
		end = ((c = get(in)) == -1);
		if (!end) {
			buf[len++] = c;
			if (len <= 1) continue;
		}

		if (repeat) {
			if (buf[len - 1] != buf[len - 2])
				repeat = 0;
			if (!repeat || len == 129 || end) {
				
				put(out, end ? len : len - 1);
				put(out, buf[0]);
				buf[0] = buf[len - 1];
				len = 1;
			}
		} else {
			if (buf[len - 1] == buf[len - 2]) {
				repeat = 1;
				if (len > 2) {
					output(out, buf, len - 2);
					buf[0] = buf[1] = buf[len - 1];
					len = 2;
				}
				continue;
			}
			if (len == 128 || end) {
				output(out, buf, len);
				len = 0;
				repeat = 0;
			}
		}
	}
	put(out, -1);
}

void decode(stream in, stream out)
{
	int c, i, cnt;
	while (1) {
		c = in->get(in);
		if (c == -1) return;
		if (c > 128) {
			cnt = c - 128;
			for (i = 0; i < cnt; i++)
				out->put(out, in->get(in));
		} else {
			cnt = c;
			c = in->get(in);
			for (i = 0; i < cnt; i++)
				out->put(out, c);
		}
	}
}

int main()
{
	char buf[256];
	string_stream str_in = { sget, 0,
		"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW", 0};
	string_stream str_out = { sget, sput, buf, 0 };
	file_stream file = { 0, file_put, stdout };

	
	encode((stream)&str_in, (stream)&str_out);

	
	decode((stream)&str_out, (stream)&file);

	return 0;
}

Python: def encode(input_string):
    count = 1
    prev = None
    lst = []
    for character in input_string:
        if character != prev:
            if prev:
                entry = (prev, count)
                lst.append(entry)
            count = 1
            prev = character
        else:
            count += 1
    else:
        try:
            entry = (character, count)
            lst.append(entry)
            return (lst, 0)
        except Exception as e:
            print("Exception encountered {e}".format(e=e)) 
            return (e, 1)
 
def decode(lst):
    q = []
    for character, count in lst:
        q.append(character * count)
    return ''.join(q)
 

value = encode("aaaaahhhhhhmmmmmmmuiiiiiiiaaaaaa")
if value[1] == 0:
    print("Encoded value is {}".format(value[0]))
    decode(value[0])