mystr = "ABBBCCDDZ"

def get_iterparts(mystr):
    buf = ""
    for char in mystr:
        if not buf or buf.endswith(char):
            buf += char
        else:
            yield buf
            buf = char
    if buf:
        yield buf
print list(get_iterparts(mystr))

def get_parts(mystr):
    parts = []
    buf = ""
    for char in mystr:
        if not buf or buf.endswith(char):
            buf += char
        else:
            parts.append(buf)
            buf = char
    if buf:
        parts.append(buf)
    return parts
print get_parts(mystr)