What is the Pythonic way to implement a simple FSM?

Question

Yesterday I had to parse a very simple binary data file - the rule is, look for two bytes in a row that are both 0xAA, then the next byte will be a length byte, then skip 9 byte

Answer 1

You can use regexps. Something like this code will find the first block of data. Then it's just a case of starting the next search from after the previous match.

find_header = re.compile('\xaa\xaa(.).{9}', re.DOTALL)
m = find_header.search(input_text)
if m:
    length = chr(find_header.group(1))
    data = input_text[m.end():m.end() + length]